diff --git a/src/ol/Feature.js b/src/ol/Feature.js
index bb26cb86d3..53d6bedcf6 100644
--- a/src/ol/Feature.js
+++ b/src/ol/Feature.js
@@ -1,7 +1,7 @@
 /**
  * @module ol/Feature
  */
-import _ol_asserts_ from './asserts.js';
+import {assert} from './asserts.js';
 import _ol_events_ from './events.js';
 import EventType from './events/EventType.js';
 import {inherits} from './index.js';
@@ -307,7 +307,7 @@ _ol_Feature_.createStyleFunction = function(obj) {
     if (Array.isArray(obj)) {
       styles = obj;
     } else {
-      _ol_asserts_.assert(obj instanceof _ol_style_Style_,
+      assert(obj instanceof _ol_style_Style_,
           41); // Expected an `ol.style.Style` or an array of `ol.style.Style`
       styles = [obj];
     }
diff --git a/src/ol/PluggableMap.js b/src/ol/PluggableMap.js
index ad6ecd202b..1bac396a62 100644
--- a/src/ol/PluggableMap.js
+++ b/src/ol/PluggableMap.js
@@ -15,7 +15,7 @@ import _ol_ObjectEventType_ from './ObjectEventType.js';
 import TileQueue from './TileQueue.js';
 import _ol_View_ from './View.js';
 import _ol_ViewHint_ from './ViewHint.js';
-import _ol_asserts_ from './asserts.js';
+import {assert} from './asserts.js';
 import {removeNode} from './dom.js';
 import _ol_events_ from './events.js';
 import Event from './events/Event.js';
@@ -1424,7 +1424,7 @@ _ol_PluggableMap_.createOptionsInternal = function(options) {
     } else if (typeof options.renderer === 'string') {
       rendererTypes = [options.renderer];
     } else {
-      _ol_asserts_.assert(false, 46); // Incorrect format for `renderer` option
+      assert(false, 46); // Incorrect format for `renderer` option
     }
     if (rendererTypes.indexOf(/** @type {ol.renderer.Type} */ ('dom')) >= 0) {
       rendererTypes = rendererTypes.concat(_ol_PluggableMap_.DEFAULT_RENDERER_TYPES);
@@ -1459,7 +1459,7 @@ _ol_PluggableMap_.createOptionsInternal = function(options) {
     if (Array.isArray(options.controls)) {
       controls = new _ol_Collection_(options.controls.slice());
     } else {
-      _ol_asserts_.assert(options.controls instanceof _ol_Collection_,
+      assert(options.controls instanceof _ol_Collection_,
           47); // Expected `controls` to be an array or an `ol.Collection`
       controls = options.controls;
     }
@@ -1470,7 +1470,7 @@ _ol_PluggableMap_.createOptionsInternal = function(options) {
     if (Array.isArray(options.interactions)) {
       interactions = new _ol_Collection_(options.interactions.slice());
     } else {
-      _ol_asserts_.assert(options.interactions instanceof _ol_Collection_,
+      assert(options.interactions instanceof _ol_Collection_,
           48); // Expected `interactions` to be an array or an `ol.Collection`
       interactions = options.interactions;
     }
@@ -1481,7 +1481,7 @@ _ol_PluggableMap_.createOptionsInternal = function(options) {
     if (Array.isArray(options.overlays)) {
       overlays = new _ol_Collection_(options.overlays.slice());
     } else {
-      _ol_asserts_.assert(options.overlays instanceof _ol_Collection_,
+      assert(options.overlays instanceof _ol_Collection_,
           49); // Expected `overlays` to be an array or an `ol.Collection`
       overlays = options.overlays;
     }
diff --git a/src/ol/TileRange.js b/src/ol/TileRange.js
index 1359443a58..b4bed1f182 100644
--- a/src/ol/TileRange.js
+++ b/src/ol/TileRange.js
@@ -12,7 +12,7 @@
  * @param {number} maxY Maximum Y.
  * @struct
  */
-var _ol_TileRange_ = function(minX, maxX, minY, maxY) {
+var TileRange = function(minX, maxX, minY, maxY) {
 
   /**
    * @type {number}
@@ -45,7 +45,7 @@ var _ol_TileRange_ = function(minX, maxX, minY, maxY) {
  * @param {ol.TileRange|undefined} tileRange TileRange.
  * @return {ol.TileRange} Tile range.
  */
-_ol_TileRange_.createOrUpdate = function(minX, maxX, minY, maxY, tileRange) {
+TileRange.createOrUpdate = function(minX, maxX, minY, maxY, tileRange) {
   if (tileRange !== undefined) {
     tileRange.minX = minX;
     tileRange.maxX = maxX;
@@ -53,7 +53,7 @@ _ol_TileRange_.createOrUpdate = function(minX, maxX, minY, maxY, tileRange) {
     tileRange.maxY = maxY;
     return tileRange;
   } else {
-    return new _ol_TileRange_(minX, maxX, minY, maxY);
+    return new TileRange(minX, maxX, minY, maxY);
   }
 };
 
@@ -62,7 +62,7 @@ _ol_TileRange_.createOrUpdate = function(minX, maxX, minY, maxY, tileRange) {
  * @param {ol.TileCoord} tileCoord Tile coordinate.
  * @return {boolean} Contains tile coordinate.
  */
-_ol_TileRange_.prototype.contains = function(tileCoord) {
+TileRange.prototype.contains = function(tileCoord) {
   return this.containsXY(tileCoord[1], tileCoord[2]);
 };
 
@@ -71,7 +71,7 @@ _ol_TileRange_.prototype.contains = function(tileCoord) {
  * @param {ol.TileRange} tileRange Tile range.
  * @return {boolean} Contains.
  */
-_ol_TileRange_.prototype.containsTileRange = function(tileRange) {
+TileRange.prototype.containsTileRange = function(tileRange) {
   return this.minX <= tileRange.minX && tileRange.maxX <= this.maxX &&
       this.minY <= tileRange.minY && tileRange.maxY <= this.maxY;
 };
@@ -82,7 +82,7 @@ _ol_TileRange_.prototype.containsTileRange = function(tileRange) {
  * @param {number} y Tile coordinate y.
  * @return {boolean} Contains coordinate.
  */
-_ol_TileRange_.prototype.containsXY = function(x, y) {
+TileRange.prototype.containsXY = function(x, y) {
   return this.minX <= x && x <= this.maxX && this.minY <= y && y <= this.maxY;
 };
 
@@ -91,7 +91,7 @@ _ol_TileRange_.prototype.containsXY = function(x, y) {
  * @param {ol.TileRange} tileRange Tile range.
  * @return {boolean} Equals.
  */
-_ol_TileRange_.prototype.equals = function(tileRange) {
+TileRange.prototype.equals = function(tileRange) {
   return this.minX == tileRange.minX && this.minY == tileRange.minY &&
       this.maxX == tileRange.maxX && this.maxY == tileRange.maxY;
 };
@@ -100,7 +100,7 @@ _ol_TileRange_.prototype.equals = function(tileRange) {
 /**
  * @param {ol.TileRange} tileRange Tile range.
  */
-_ol_TileRange_.prototype.extend = function(tileRange) {
+TileRange.prototype.extend = function(tileRange) {
   if (tileRange.minX < this.minX) {
     this.minX = tileRange.minX;
   }
@@ -119,7 +119,7 @@ _ol_TileRange_.prototype.extend = function(tileRange) {
 /**
  * @return {number} Height.
  */
-_ol_TileRange_.prototype.getHeight = function() {
+TileRange.prototype.getHeight = function() {
   return this.maxY - this.minY + 1;
 };
 
@@ -127,7 +127,7 @@ _ol_TileRange_.prototype.getHeight = function() {
 /**
  * @return {ol.Size} Size.
  */
-_ol_TileRange_.prototype.getSize = function() {
+TileRange.prototype.getSize = function() {
   return [this.getWidth(), this.getHeight()];
 };
 
@@ -135,7 +135,7 @@ _ol_TileRange_.prototype.getSize = function() {
 /**
  * @return {number} Width.
  */
-_ol_TileRange_.prototype.getWidth = function() {
+TileRange.prototype.getWidth = function() {
   return this.maxX - this.minX + 1;
 };
 
@@ -144,10 +144,10 @@ _ol_TileRange_.prototype.getWidth = function() {
  * @param {ol.TileRange} tileRange Tile range.
  * @return {boolean} Intersects.
  */
-_ol_TileRange_.prototype.intersects = function(tileRange) {
+TileRange.prototype.intersects = function(tileRange) {
   return this.minX <= tileRange.maxX &&
       this.maxX >= tileRange.minX &&
       this.minY <= tileRange.maxY &&
       this.maxY >= tileRange.minY;
 };
-export default _ol_TileRange_;
+export default TileRange;
diff --git a/src/ol/VectorImageTile.js b/src/ol/VectorImageTile.js
index efe32da257..d6ad4abb4e 100644
--- a/src/ol/VectorImageTile.js
+++ b/src/ol/VectorImageTile.js
@@ -8,7 +8,7 @@ import {createCanvasContext2D} from './dom.js';
 import _ol_events_ from './events.js';
 import {getHeight, getIntersection, getWidth} from './extent.js';
 import EventType from './events/EventType.js';
-import _ol_featureloader_ from './featureloader.js';
+import {loadFeaturesXhr} from './featureloader.js';
 
 /**
  * @constructor
@@ -292,9 +292,7 @@ _ol_VectorImageTile_.prototype.finishLoading_ = function() {
  * @param {string} url URL.
  */
 _ol_VectorImageTile_.defaultLoadFunction = function(tile, url) {
-  var loader = _ol_featureloader_.loadFeaturesXhr(
-      url, tile.getFormat(), tile.onLoad.bind(tile), tile.onError.bind(tile));
-
+  var loader = loadFeaturesXhr(url, tile.getFormat(), tile.onLoad.bind(tile), tile.onError.bind(tile));
   tile.setLoader(loader);
 };
 export default _ol_VectorImageTile_;
diff --git a/src/ol/View.js b/src/ol/View.js
index f782221896..24f0fef8d4 100644
--- a/src/ol/View.js
+++ b/src/ol/View.js
@@ -10,7 +10,7 @@ import _ol_RotationConstraint_ from './RotationConstraint.js';
 import _ol_ViewHint_ from './ViewHint.js';
 import _ol_ViewProperty_ from './ViewProperty.js';
 import _ol_array_ from './array.js';
-import _ol_asserts_ from './asserts.js';
+import {assert} from './asserts.js';
 import _ol_coordinate_ from './coordinate.js';
 import {inAndOut} from './easing.js';
 import {getForViewAndSize, getCenter, getHeight, getWidth, isEmpty} from './extent.js';
@@ -608,11 +608,11 @@ _ol_View_.prototype.getHints = function(opt_hints) {
 _ol_View_.prototype.calculateExtent = function(opt_size) {
   var size = opt_size || this.getSizeFromViewport_();
   var center = /** @type {!ol.Coordinate} */ (this.getCenter());
-  _ol_asserts_.assert(center, 1); // The view center is not defined
+  assert(center, 1); // The view center is not defined
   var resolution = /** @type {!number} */ (this.getResolution());
-  _ol_asserts_.assert(resolution !== undefined, 2); // The view resolution is not defined
+  assert(resolution !== undefined, 2); // The view resolution is not defined
   var rotation = /** @type {!number} */ (this.getRotation());
-  _ol_asserts_.assert(rotation !== undefined, 3); // The view rotation is not defined
+  assert(rotation !== undefined, 3); // The view rotation is not defined
 
   return getForViewAndSize(center, resolution, rotation, size);
 };
@@ -880,9 +880,9 @@ _ol_View_.prototype.fit = function(geometryOrExtent, opt_options) {
   /** @type {ol.geom.SimpleGeometry} */
   var geometry;
   if (!(geometryOrExtent instanceof SimpleGeometry)) {
-    _ol_asserts_.assert(Array.isArray(geometryOrExtent),
+    assert(Array.isArray(geometryOrExtent),
         24); // Invalid extent or geometry provided as `geometry`
-    _ol_asserts_.assert(!isEmpty(geometryOrExtent),
+    assert(!isEmpty(geometryOrExtent),
         25); // Cannot fit empty extent provided as `geometry`
     geometry = Polygon.fromExtent(geometryOrExtent);
   } else if (geometryOrExtent.getType() === GeometryType.CIRCLE) {
diff --git a/src/ol/asserts.js b/src/ol/asserts.js
index 626f95d744..0521164703 100644
--- a/src/ol/asserts.js
+++ b/src/ol/asserts.js
@@ -2,16 +2,13 @@
  * @module ol/asserts
  */
 import AssertionError from './AssertionError.js';
-var _ol_asserts_ = {};
-
 
 /**
  * @param {*} assertion Assertion we expected to be truthy.
  * @param {number} errorCode Error code.
  */
-_ol_asserts_.assert = function(assertion, errorCode) {
+export function assert(assertion, errorCode) {
   if (!assertion) {
     throw new AssertionError(errorCode);
   }
-};
-export default _ol_asserts_;
+}
diff --git a/src/ol/color.js b/src/ol/color.js
index 398631876a..c883937a3b 100644
--- a/src/ol/color.js
+++ b/src/ol/color.js
@@ -1,7 +1,7 @@
 /**
  * @module ol/color
  */
-import _ol_asserts_ from './asserts.js';
+import {assert} from './asserts.js';
 import _ol_math_ from './math.js';
 var _ol_color_ = {};
 
@@ -173,7 +173,7 @@ _ol_color_.fromStringInternal_ = function(s) {
     parts.push(1);
     color = _ol_color_.normalize(parts);
   } else {
-    _ol_asserts_.assert(false, 14); // Invalid color
+    assert(false, 14); // Invalid color
   }
   return /** @type {ol.Color} */ (color);
 };
diff --git a/src/ol/control/ScaleLine.js b/src/ol/control/ScaleLine.js
index d4cd6dc8ee..7e1ba55b3c 100644
--- a/src/ol/control/ScaleLine.js
+++ b/src/ol/control/ScaleLine.js
@@ -3,7 +3,7 @@
  */
 import {inherits} from '../index.js';
 import _ol_Object_ from '../Object.js';
-import _ol_asserts_ from '../asserts.js';
+import {assert} from '../asserts.js';
 import Control from '../control/Control.js';
 import ScaleLineUnits from '../control/ScaleLineUnits.js';
 import _ol_css_ from '../css.js';
@@ -237,7 +237,7 @@ ScaleLine.prototype.updateElement_ = function() {
       pointResolution /= 1609.3472;
     }
   } else {
-    _ol_asserts_.assert(false, 33); // Invalid units
+    assert(false, 33); // Invalid units
   }
 
   var i = 3 * Math.floor(
diff --git a/src/ol/events/condition.js b/src/ol/events/condition.js
index d19479114a..299526a004 100644
--- a/src/ol/events/condition.js
+++ b/src/ol/events/condition.js
@@ -2,7 +2,7 @@
  * @module ol/events/condition
  */
 import MapBrowserEventType from '../MapBrowserEventType.js';
-import _ol_asserts_ from '../asserts.js';
+import {assert} from '../asserts.js';
 import {TRUE, FALSE} from '../functions.js';
 import _ol_has_ from '../has.js';
 var _ol_events_condition_ = {};
@@ -206,7 +206,7 @@ _ol_events_condition_.targetNotEditable = function(mapBrowserEvent) {
  * @api
  */
 _ol_events_condition_.mouseOnly = function(mapBrowserEvent) {
-  _ol_asserts_.assert(mapBrowserEvent.pointerEvent, 56); // mapBrowserEvent must originate from a pointer event
+  assert(mapBrowserEvent.pointerEvent, 56); // mapBrowserEvent must originate from a pointer event
   // see http://www.w3.org/TR/pointerevents/#widl-PointerEvent-pointerType
   return /** @type {ol.MapBrowserEvent} */ (mapBrowserEvent).pointerEvent.pointerType == 'mouse';
 };
diff --git a/src/ol/featureloader.js b/src/ol/featureloader.js
index 359e0c245a..714c8d056c 100644
--- a/src/ol/featureloader.js
+++ b/src/ol/featureloader.js
@@ -4,7 +4,6 @@
 import {nullFunction} from './index.js';
 import _ol_format_FormatType_ from './format/FormatType.js';
 import _ol_xml_ from './xml.js';
-var _ol_featureloader_ = {};
 
 
 /**
@@ -18,7 +17,7 @@ var _ol_featureloader_ = {};
  *     source as `this`.
  * @return {ol.FeatureLoader} The feature loader.
  */
-_ol_featureloader_.loadFeaturesXhr = function(url, format, success, failure) {
+export function loadFeaturesXhr(url, format, success, failure) {
   return (
     /**
      * @param {ol.Extent} extent Extent.
@@ -75,7 +74,7 @@ _ol_featureloader_.loadFeaturesXhr = function(url, format, success, failure) {
       xhr.send();
     }
   );
-};
+}
 
 
 /**
@@ -87,8 +86,8 @@ _ol_featureloader_.loadFeaturesXhr = function(url, format, success, failure) {
  * @return {ol.FeatureLoader} The feature loader.
  * @api
  */
-_ol_featureloader_.xhr = function(url, format) {
-  return _ol_featureloader_.loadFeaturesXhr(url, format,
+export function xhr(url, format) {
+  return loadFeaturesXhr(url, format,
       /**
        * @param {Array.<ol.Feature>} features The loaded features.
        * @param {ol.proj.Projection} dataProjection Data projection.
@@ -97,5 +96,4 @@ _ol_featureloader_.xhr = function(url, format) {
       function(features, dataProjection) {
         this.addFeatures(features);
       }, /* FIXME handle error */ nullFunction);
-};
-export default _ol_featureloader_;
+}
diff --git a/src/ol/format/EsriJSON.js b/src/ol/format/EsriJSON.js
index f91049d7fb..4079d18990 100644
--- a/src/ol/format/EsriJSON.js
+++ b/src/ol/format/EsriJSON.js
@@ -3,7 +3,7 @@
  */
 import {inherits} from '../index.js';
 import _ol_Feature_ from '../Feature.js';
-import _ol_asserts_ from '../asserts.js';
+import {assert} from '../asserts.js';
 import {containsExtent} from '../extent.js';
 import FeatureFormat from '../format/Feature.js';
 import JSONFeature from '../format/JSONFeature.js';
@@ -277,7 +277,7 @@ EsriJSON.writePointGeometry_ = function(geometry, opt_options) {
       y: coordinates[1]
     });
   } else {
-    _ol_asserts_.assert(false, 34); // Invalid geometry layout
+    assert(false, 34); // Invalid geometry layout
   }
   return /** @type {EsriJSONGeometry} */ (esriJSON);
 };
diff --git a/src/ol/format/GeoJSON.js b/src/ol/format/GeoJSON.js
index bd9c4eeb79..33304493a0 100644
--- a/src/ol/format/GeoJSON.js
+++ b/src/ol/format/GeoJSON.js
@@ -5,7 +5,7 @@
 // see https://github.com/openlayers/openlayers/issues/2078
 
 import {inherits} from '../index.js';
-import _ol_asserts_ from '../asserts.js';
+import {assert} from '../asserts.js';
 import _ol_Feature_ from '../Feature.js';
 import FeatureFormat from '../format/Feature.js';
 import JSONFeature from '../format/JSONFeature.js';
@@ -469,7 +469,7 @@ GeoJSON.prototype.readProjectionFromObject = function(object) {
     if (crs.type == 'name') {
       projection = getProjection(crs.properties.name);
     } else {
-      _ol_asserts_.assert(false, 36); // Unknown SRS type
+      assert(false, 36); // Unknown SRS type
     }
   } else {
     projection = this.defaultDataProjection;
diff --git a/src/ol/format/KML.js b/src/ol/format/KML.js
index c5087535e9..984e5f2dce 100644
--- a/src/ol/format/KML.js
+++ b/src/ol/format/KML.js
@@ -4,7 +4,7 @@
 import {inherits} from '../index.js';
 import _ol_Feature_ from '../Feature.js';
 import _ol_array_ from '../array.js';
-import _ol_asserts_ from '../asserts.js';
+import {assert} from '../asserts.js';
 import _ol_color_ from '../color.js';
 import FeatureFormat from '../format/Feature.js';
 import XMLFeature from '../format/XMLFeature.js';
@@ -945,7 +945,7 @@ KML.readMultiGeometry_ = function(node, objectStack) {
     } else if (type == GeometryType.GEOMETRY_COLLECTION) {
       multiGeometry = new GeometryCollection(geometries);
     } else {
-      _ol_asserts_.assert(false, 37); // Unknown geometry type found
+      assert(false, 37); // Unknown geometry type found
     }
   } else {
     multiGeometry = new GeometryCollection(geometries);
@@ -1171,7 +1171,7 @@ KML.PlacemarkStyleMapParser_ = function(node, objectStack) {
   } else if (typeof styleMapValue === 'string') {
     placemarkObject['styleUrl'] = styleMapValue;
   } else {
-    _ol_asserts_.assert(false, 38); // `styleMapValue` has an unknown type
+    assert(false, 38); // `styleMapValue` has an unknown type
   }
 };
 
@@ -2124,7 +2124,7 @@ KML.writeCoordinatesTextNode_ = function(node, coordinates, objectStack) {
       layout == GeometryLayout.XYZM) {
     dimension = 3;
   } else {
-    _ol_asserts_.assert(false, 34); // Invalid geometry layout
+    assert(false, 34); // Invalid geometry layout
   }
 
   var d, i;
@@ -2382,7 +2382,7 @@ KML.writeMultiGeometry_ = function(node, geometry, objectStack) {
         (/** @type {ol.geom.MultiPolygon} */ (geometry)).getPolygons();
     factory = KML.POLYGON_NODE_FACTORY_;
   } else {
-    _ol_asserts_.assert(false, 39); // Unknown geometry type
+    assert(false, 39); // Unknown geometry type
   }
   _ol_xml_.pushSerializeAndPop(context,
       KML.MULTI_GEOMETRY_SERIALIZERS_, factory,
diff --git a/src/ol/format/MVT.js b/src/ol/format/MVT.js
index 08ff917c84..162ca43094 100644
--- a/src/ol/format/MVT.js
+++ b/src/ol/format/MVT.js
@@ -4,7 +4,7 @@
 //FIXME Implement projection handling
 
 import {inherits} from '../index.js';
-import _ol_asserts_ from '../asserts.js';
+import {assert} from '../asserts.js';
 import PBF from 'pbf';
 import FeatureFormat from '../format/Feature.js';
 import _ol_format_FormatType_ from '../format/FormatType.js';
@@ -225,7 +225,7 @@ MVT.readRawGeometry_ = function(pbf, feature, flatCoordinates, ends) {
       }
 
     } else {
-      _ol_asserts_.assert(false, 59); // Invalid command found in the PBF
+      assert(false, 59); // Invalid command found in the PBF
     }
   }
 
diff --git a/src/ol/format/Polyline.js b/src/ol/format/Polyline.js
index 282be5f3b5..cfc1ff618d 100644
--- a/src/ol/format/Polyline.js
+++ b/src/ol/format/Polyline.js
@@ -2,7 +2,7 @@
  * @module ol/format/Polyline
  */
 import {inherits} from '../index.js';
-import _ol_asserts_ from '../asserts.js';
+import {assert} from '../asserts.js';
 import _ol_Feature_ from '../Feature.js';
 import FeatureFormat from '../format/Feature.js';
 import TextFeature from '../format/TextFeature.js';
@@ -359,7 +359,7 @@ Polyline.prototype.writeFeatureText = function(feature, opt_options) {
   if (geometry) {
     return this.writeGeometryText(geometry, opt_options);
   } else {
-    _ol_asserts_.assert(false, 40); // Expected `feature` to have a geometry
+    assert(false, 40); // Expected `feature` to have a geometry
     return '';
   }
 };
diff --git a/src/ol/format/WFS.js b/src/ol/format/WFS.js
index ebdad61b0e..1db5e78776 100644
--- a/src/ol/format/WFS.js
+++ b/src/ol/format/WFS.js
@@ -2,7 +2,7 @@
  * @module ol/format/WFS
  */
 import {inherits} from '../index.js';
-import _ol_asserts_ from '../asserts.js';
+import {assert} from '../asserts.js';
 import GML2 from '../format/GML2.js';
 import GML3 from '../format/GML3.js';
 import GMLBase from '../format/GMLBase.js';
@@ -450,7 +450,7 @@ WFS.getTypeName_ = function(featurePrefix, featureType) {
  */
 WFS.writeDelete_ = function(node, feature, objectStack) {
   var context = objectStack[objectStack.length - 1];
-  _ol_asserts_.assert(feature.getId() !== undefined, 26); // Features must have an id set
+  assert(feature.getId() !== undefined, 26); // Features must have an id set
   var featureType = context['featureType'];
   var featurePrefix = context['featurePrefix'];
   var featureNS = context['featureNS'];
@@ -473,7 +473,7 @@ WFS.writeDelete_ = function(node, feature, objectStack) {
  */
 WFS.writeUpdate_ = function(node, feature, objectStack) {
   var context = objectStack[objectStack.length - 1];
-  _ol_asserts_.assert(feature.getId() !== undefined, 27); // Features must have an id set
+  assert(feature.getId() !== undefined, 27); // Features must have an id set
   var featureType = context['featureType'];
   var featurePrefix = context['featurePrefix'];
   var featureNS = context['featureNS'];
@@ -958,7 +958,7 @@ WFS.prototype.writeGetFeature = function(options) {
     }
     filter = options.filter;
     if (options.bbox) {
-      _ol_asserts_.assert(options.geometryName,
+      assert(options.geometryName,
           12); // `options.geometryName` must also be provided when `options.bbox` is set
       var bbox = _ol_format_filter_.bbox(
           /** @type {string} */ (options.geometryName), options.bbox, options.srsName);
@@ -982,7 +982,7 @@ WFS.prototype.writeGetFeature = function(options) {
     'filter': filter,
     'propertyNames': options.propertyNames ? options.propertyNames : []
   };
-  _ol_asserts_.assert(Array.isArray(options.featureTypes),
+  assert(Array.isArray(options.featureTypes),
       11); // `options.featureTypes` should be an Array
   WFS.writeGetFeature_(node, /** @type {!Array.<string>} */ (options.featureTypes), [context]);
   return node;
diff --git a/src/ol/format/filter/LogicalNary.js b/src/ol/format/filter/LogicalNary.js
index 082591ff29..054d540e74 100644
--- a/src/ol/format/filter/LogicalNary.js
+++ b/src/ol/format/filter/LogicalNary.js
@@ -2,7 +2,7 @@
  * @module ol/format/filter/LogicalNary
  */
 import {inherits} from '../../index.js';
-import _ol_asserts_ from '../../asserts.js';
+import {assert} from '../../asserts.js';
 import Filter from '../filter/Filter.js';
 
 /**
@@ -25,7 +25,7 @@ var LogicalNary = function(tagName, conditions) {
    * @type {Array.<ol.format.filter.Filter>}
    */
   this.conditions = Array.prototype.slice.call(arguments, 1);
-  _ol_asserts_.assert(this.conditions.length >= 2, 57); // At least 2 conditions are required.
+  assert(this.conditions.length >= 2, 57); // At least 2 conditions are required.
 };
 
 inherits(LogicalNary, Filter);
diff --git a/src/ol/layer/Group.js b/src/ol/layer/Group.js
index b1327bd8be..b6c30bc66f 100644
--- a/src/ol/layer/Group.js
+++ b/src/ol/layer/Group.js
@@ -6,7 +6,7 @@ import _ol_Collection_ from '../Collection.js';
 import _ol_CollectionEventType_ from '../CollectionEventType.js';
 import _ol_Object_ from '../Object.js';
 import _ol_ObjectEventType_ from '../ObjectEventType.js';
-import _ol_asserts_ from '../asserts.js';
+import {assert} from '../asserts.js';
 import _ol_events_ from '../events.js';
 import EventType from '../events/EventType.js';
 import {getIntersection} from '../extent.js';
@@ -56,7 +56,7 @@ var _ol_layer_Group_ = function(opt_options) {
     if (Array.isArray(layers)) {
       layers = new _ol_Collection_(layers.slice(), {unique: true});
     } else {
-      _ol_asserts_.assert(layers instanceof _ol_Collection_,
+      assert(layers instanceof _ol_Collection_,
           43); // Expected `layers` to be an array or an `ol.Collection`
       layers = layers;
     }
diff --git a/src/ol/layer/VectorTile.js b/src/ol/layer/VectorTile.js
index 3d11211b0a..828d5b7e3b 100644
--- a/src/ol/layer/VectorTile.js
+++ b/src/ol/layer/VectorTile.js
@@ -3,7 +3,7 @@
  */
 import {inherits} from '../index.js';
 import _ol_LayerType_ from '../LayerType.js';
-import _ol_asserts_ from '../asserts.js';
+import {assert} from '../asserts.js';
 import _ol_layer_TileProperty_ from '../layer/TileProperty.js';
 import _ol_layer_Vector_ from '../layer/Vector.js';
 import _ol_layer_VectorTileRenderType_ from '../layer/VectorTileRenderType.js';
@@ -25,7 +25,7 @@ var _ol_layer_VectorTile_ = function(opt_options) {
   var options = opt_options ? opt_options : {};
 
   var renderMode = options.renderMode || _ol_layer_VectorTileRenderType_.HYBRID;
-  _ol_asserts_.assert(renderMode == undefined ||
+  assert(renderMode == undefined ||
       renderMode == _ol_layer_VectorTileRenderType_.IMAGE ||
       renderMode == _ol_layer_VectorTileRenderType_.HYBRID ||
       renderMode == _ol_layer_VectorTileRenderType_.VECTOR,
diff --git a/src/ol/math.js b/src/ol/math.js
index a1aba72bb7..03f707832c 100644
--- a/src/ol/math.js
+++ b/src/ol/math.js
@@ -1,7 +1,7 @@
 /**
  * @module ol/math
  */
-import _ol_asserts_ from './asserts.js';
+import {assert} from './asserts.js';
 var _ol_math_ = {};
 
 
@@ -50,7 +50,7 @@ _ol_math_.cosh = (function() {
  * @return {number} The smallest power of two greater than or equal to x.
  */
 _ol_math_.roundUpToPowerOfTwo = function(x) {
-  _ol_asserts_.assert(0 < x, 29); // `x` must be greater than `0`
+  assert(0 < x, 29); // `x` must be greater than `0`
   return Math.pow(2, Math.ceil(Math.log(x) / Math.LN2));
 };
 
diff --git a/src/ol/renderer/canvas/TileLayer.js b/src/ol/renderer/canvas/TileLayer.js
index c323752b6c..1615fb4e6f 100644
--- a/src/ol/renderer/canvas/TileLayer.js
+++ b/src/ol/renderer/canvas/TileLayer.js
@@ -3,7 +3,7 @@
  */
 import {getUid, inherits} from '../../index.js';
 import _ol_LayerType_ from '../../LayerType.js';
-import _ol_TileRange_ from '../../TileRange.js';
+import TileRange from '../../TileRange.js';
 import _ol_TileState_ from '../../TileState.js';
 import _ol_ViewHint_ from '../../ViewHint.js';
 import {createCanvasContext2D} from '../../dom.js';
@@ -62,7 +62,7 @@ var _ol_renderer_canvas_TileLayer_ = function(tileLayer) {
    * @private
    * @type {ol.TileRange}
    */
-  this.tmpTileRange_ = new _ol_TileRange_(0, 0, 0, 0);
+  this.tmpTileRange_ = new TileRange(0, 0, 0, 0);
 
   /**
    * @private
diff --git a/src/ol/renderer/webgl/TileLayer.js b/src/ol/renderer/webgl/TileLayer.js
index 2cdb5a7da6..648f72e8ad 100644
--- a/src/ol/renderer/webgl/TileLayer.js
+++ b/src/ol/renderer/webgl/TileLayer.js
@@ -6,7 +6,7 @@
 
 import {inherits} from '../../index.js';
 import _ol_LayerType_ from '../../LayerType.js';
-import _ol_TileRange_ from '../../TileRange.js';
+import TileRange from '../../TileRange.js';
 import _ol_TileState_ from '../../TileState.js';
 import _ol_array_ from '../../array.js';
 import {createEmpty, intersects} from '../../extent.js';
@@ -247,7 +247,7 @@ _ol_renderer_webgl_TileLayer_.prototype.prepareFrame = function(frameState, laye
     var useInterimTilesOnError = tileLayer.getUseInterimTilesOnError();
     var allTilesLoaded = true;
     var tmpExtent = createEmpty();
-    var tmpTileRange = new _ol_TileRange_(0, 0, 0, 0);
+    var tmpTileRange = new TileRange(0, 0, 0, 0);
     var childTileRange, drawable, fullyLoaded, tile, tileState;
     var x, y, tileExtent;
     for (x = tileRange.minX; x <= tileRange.maxX; ++x) {
diff --git a/src/ol/source/Cluster.js b/src/ol/source/Cluster.js
index c0f0415182..55c8ce2eee 100644
--- a/src/ol/source/Cluster.js
+++ b/src/ol/source/Cluster.js
@@ -3,7 +3,7 @@
  */
 
 import {getUid, inherits} from '../index.js';
-import _ol_asserts_ from '../asserts.js';
+import {assert} from '../asserts.js';
 import _ol_Feature_ from '../Feature.js';
 import _ol_coordinate_ from '../coordinate.js';
 import EventType from '../events/EventType.js';
@@ -55,7 +55,7 @@ var _ol_source_Cluster_ = function(options) {
    */
   this.geometryFunction = options.geometryFunction || function(feature) {
     var geometry = /** @type {ol.geom.Point} */ (feature.getGeometry());
-    _ol_asserts_.assert(geometry instanceof Point,
+    assert(geometry instanceof Point,
         10); // The default `geometryFunction` can only handle `ol.geom.Point` geometries
     return geometry;
   };
diff --git a/src/ol/source/ImageArcGISRest.js b/src/ol/source/ImageArcGISRest.js
index 752939d9fe..ca9092dbf0 100644
--- a/src/ol/source/ImageArcGISRest.js
+++ b/src/ol/source/ImageArcGISRest.js
@@ -3,7 +3,7 @@
  */
 import {inherits} from '../index.js';
 import _ol_Image_ from '../Image.js';
-import _ol_asserts_ from '../asserts.js';
+import {assert} from '../asserts.js';
 import _ol_events_ from '../events.js';
 import EventType from '../events/EventType.js';
 import {containsExtent, getHeight, getWidth} from '../extent.js';
@@ -216,7 +216,7 @@ _ol_source_ImageArcGISRest_.prototype.getRequestUrl_ = function(extent, size, pi
       .replace(/MapServer\/?$/, 'MapServer/export')
       .replace(/ImageServer\/?$/, 'ImageServer/exportImage');
   if (modifiedUrl == url) {
-    _ol_asserts_.assert(false, 50); // `options.featureTypes` should be an Array
+    assert(false, 50); // `options.featureTypes` should be an Array
   }
   return _ol_uri_.appendParams(modifiedUrl, params);
 };
diff --git a/src/ol/source/ImageWMS.js b/src/ol/source/ImageWMS.js
index d763549291..685f8d941e 100644
--- a/src/ol/source/ImageWMS.js
+++ b/src/ol/source/ImageWMS.js
@@ -5,7 +5,7 @@
 import {DEFAULT_WMS_VERSION} from './common.js';
 import {inherits} from '../index.js';
 import _ol_Image_ from '../Image.js';
-import _ol_asserts_ from '../asserts.js';
+import {assert} from '../asserts.js';
 import _ol_events_ from '../events.js';
 import EventType from '../events/EventType.js';
 import {containsExtent, getCenter, getForViewAndSize, getHeight, getWidth} from '../extent.js';
@@ -265,7 +265,7 @@ _ol_source_ImageWMS_.prototype.getImageLoadFunction = function() {
  */
 _ol_source_ImageWMS_.prototype.getRequestUrl_ = function(extent, size, pixelRatio, projection, params) {
 
-  _ol_asserts_.assert(this.url_ !== undefined, 9); // `url` must be configured or set using `#setUrl()`
+  assert(this.url_ !== undefined, 9); // `url` must be configured or set using `#setUrl()`
 
   params[this.v13_ ? 'CRS' : 'SRS'] = projection.getCode();
 
@@ -291,7 +291,7 @@ _ol_source_ImageWMS_.prototype.getRequestUrl_ = function(extent, size, pixelRati
         params['DPI'] = 90 * pixelRatio;
         break;
       default:
-        _ol_asserts_.assert(false, 8); // Unknown `serverType` configured
+        assert(false, 8); // Unknown `serverType` configured
         break;
     }
   }
diff --git a/src/ol/source/TileJSON.js b/src/ol/source/TileJSON.js
index e4f1e59d2d..b135952a59 100644
--- a/src/ol/source/TileJSON.js
+++ b/src/ol/source/TileJSON.js
@@ -9,7 +9,7 @@
 
 import {inherits} from '../index.js';
 import {createFromTemplates} from '../tileurlfunction.js';
-import _ol_asserts_ from '../asserts.js';
+import {assert} from '../asserts.js';
 import {applyTransform, intersects} from '../extent.js';
 import _ol_net_ from '../net.js';
 import {get as getProjection, getTransformFromProjections} from '../proj.js';
@@ -60,7 +60,7 @@ var _ol_source_TileJSON_ = function(options) {
   } else if (options.tileJSON) {
     this.handleTileJSONResponse(options.tileJSON);
   } else {
-    _ol_asserts_.assert(false, 51); // Either `url` or `tileJSON` options must be provided
+    assert(false, 51); // Either `url` or `tileJSON` options must be provided
   }
 
 };
diff --git a/src/ol/source/TileUTFGrid.js b/src/ol/source/TileUTFGrid.js
index 718d1feabb..6a20f53155 100644
--- a/src/ol/source/TileUTFGrid.js
+++ b/src/ol/source/TileUTFGrid.js
@@ -5,7 +5,7 @@ import {inherits} from '../index.js';
 import _ol_Tile_ from '../Tile.js';
 import _ol_TileState_ from '../TileState.js';
 import {createFromTemplates, nullTileUrlFunction} from '../tileurlfunction.js';
-import _ol_asserts_ from '../asserts.js';
+import {assert} from '../asserts.js';
 import _ol_events_ from '../events.js';
 import EventType from '../events/EventType.js';
 import {applyTransform, intersects} from '../extent.js';
@@ -70,7 +70,7 @@ var _ol_source_TileUTFGrid_ = function(options) {
   } else if (options.tileJSON) {
     this.handleTileJSONResponse(options.tileJSON);
   } else {
-    _ol_asserts_.assert(false, 51); // Either `url` or `tileJSON` options must be provided
+    assert(false, 51); // Either `url` or `tileJSON` options must be provided
   }
 };
 
diff --git a/src/ol/source/TileWMS.js b/src/ol/source/TileWMS.js
index a199dd61c1..4c1dc5bc47 100644
--- a/src/ol/source/TileWMS.js
+++ b/src/ol/source/TileWMS.js
@@ -4,7 +4,7 @@
 
 import {DEFAULT_WMS_VERSION} from './common.js';
 import {inherits} from '../index.js';
-import _ol_asserts_ from '../asserts.js';
+import {assert} from '../asserts.js';
 import {buffer, createEmpty} from '../extent.js';
 import _ol_obj_ from '../obj.js';
 import _ol_math_ from '../math.js';
@@ -225,7 +225,7 @@ _ol_source_TileWMS_.prototype.getRequestUrl_ = function(tileCoord, tileSize, til
         params['DPI'] = 90 * pixelRatio;
         break;
       default:
-        _ol_asserts_.assert(false, 52); // Unknown `serverType` configured
+        assert(false, 52); // Unknown `serverType` configured
         break;
     }
   }
diff --git a/src/ol/source/Vector.js b/src/ol/source/Vector.js
index 6d330303af..e090179ce3 100644
--- a/src/ol/source/Vector.js
+++ b/src/ol/source/Vector.js
@@ -7,12 +7,12 @@ import _ol_Collection_ from '../Collection.js';
 import _ol_CollectionEventType_ from '../CollectionEventType.js';
 import _ol_ObjectEventType_ from '../ObjectEventType.js';
 import _ol_array_ from '../array.js';
-import _ol_asserts_ from '../asserts.js';
+import {assert} from '../asserts.js';
 import _ol_events_ from '../events.js';
 import Event from '../events/Event.js';
 import EventType from '../events/EventType.js';
 import {containsExtent, equals} from '../extent.js';
-import _ol_featureloader_ from '../featureloader.js';
+import {xhr} from '../featureloader.js';
 import {TRUE} from '../functions.js';
 import _ol_loadingstrategy_ from '../loadingstrategy.js';
 import _ol_obj_ from '../obj.js';
@@ -71,9 +71,9 @@ var _ol_source_Vector_ = function(opt_options) {
   if (options.loader !== undefined) {
     this.loader_ = options.loader;
   } else if (this.url_ !== undefined) {
-    _ol_asserts_.assert(this.format_, 7); // `format` must be set when `url` is set
+    assert(this.format_, 7); // `format` must be set when `url` is set
     // create a XHR feature loader for "url" and "format"
-    this.loader_ = _ol_featureloader_.xhr(this.url_, /** @type {ol.format.Feature} */ (this.format_));
+    this.loader_ = xhr(this.url_, /** @type {ol.format.Feature} */ (this.format_));
   }
 
   /**
@@ -228,7 +228,7 @@ _ol_source_Vector_.prototype.addToIndex_ = function(featureKey, feature) {
       valid = false;
     }
   } else {
-    _ol_asserts_.assert(!(featureKey in this.undefIdIndex_),
+    assert(!(featureKey in this.undefIdIndex_),
         30); // The passed `feature` was already added to the source
     this.undefIdIndex_[featureKey] = feature;
   }
diff --git a/src/ol/source/Zoomify.js b/src/ol/source/Zoomify.js
index cbab0a112f..86dfef8006 100644
--- a/src/ol/source/Zoomify.js
+++ b/src/ol/source/Zoomify.js
@@ -6,7 +6,7 @@ import {inherits} from '../index.js';
 import _ol_ImageTile_ from '../ImageTile.js';
 import _ol_TileState_ from '../TileState.js';
 import {expandUrl, createFromTileUrlFunctions} from '../tileurlfunction.js';
-import _ol_asserts_ from '../asserts.js';
+import {assert} from '../asserts.js';
 import {createCanvasContext2D} from '../dom.js';
 import {getTopLeft} from '../extent.js';
 import _ol_size_ from '../size.js';
@@ -62,7 +62,7 @@ var _ol_source_Zoomify_ = function(opt_options) {
       }
       break;
     default:
-      _ol_asserts_.assert(false, 53); // Unknown `tierSizeCalculation` configured
+      assert(false, 53); // Unknown `tierSizeCalculation` configured
       break;
   }
 
diff --git a/src/ol/structs/LRUCache.js b/src/ol/structs/LRUCache.js
index 810005e2fb..d3b7b2eae2 100644
--- a/src/ol/structs/LRUCache.js
+++ b/src/ol/structs/LRUCache.js
@@ -2,7 +2,7 @@
  * @module ol/structs/LRUCache
  */
 import {inherits} from '../index.js';
-import _ol_asserts_ from '../asserts.js';
+import {assert} from '../asserts.js';
 import EventTarget from '../events/EventTarget.js';
 import EventType from '../events/EventType.js';
 
@@ -107,7 +107,7 @@ LRUCache.prototype.forEach = function(f, opt_this) {
  */
 LRUCache.prototype.get = function(key) {
   var entry = this.entries_[key];
-  _ol_asserts_.assert(entry !== undefined,
+  assert(entry !== undefined,
       15); // Tried to get a value for a key that does not exist in the cache
   if (entry === this.newest_) {
     return entry.value_;
@@ -133,7 +133,7 @@ LRUCache.prototype.get = function(key) {
  */
 LRUCache.prototype.remove = function(key) {
   var entry = this.entries_[key];
-  _ol_asserts_.assert(entry !== undefined, 15); // Tried to get a value for a key that does not exist in the cache
+  assert(entry !== undefined, 15); // Tried to get a value for a key that does not exist in the cache
   if (entry === this.newest_) {
     this.newest_ = /** @type {ol.LRUCacheEntry} */ (entry.older);
     if (this.newest_) {
@@ -248,7 +248,7 @@ LRUCache.prototype.replace = function(key, value) {
  * @param {T} value Value.
  */
 LRUCache.prototype.set = function(key, value) {
-  _ol_asserts_.assert(!(key in this.entries_),
+  assert(!(key in this.entries_),
       16); // Tried to set a value for a key that is used already
   var entry = /** @type {ol.LRUCacheEntry} */ ({
     key_: key,
diff --git a/src/ol/structs/PriorityQueue.js b/src/ol/structs/PriorityQueue.js
index 6285793b55..8829c3cbc0 100644
--- a/src/ol/structs/PriorityQueue.js
+++ b/src/ol/structs/PriorityQueue.js
@@ -1,7 +1,7 @@
 /**
  * @module ol/structs/PriorityQueue
  */
-import _ol_asserts_ from '../asserts.js';
+import {assert} from '../asserts.js';
 import _ol_obj_ from '../obj.js';
 
 /**
@@ -99,7 +99,7 @@ PriorityQueue.prototype.dequeue = function() {
  * @return {boolean} The element was added to the queue.
  */
 PriorityQueue.prototype.enqueue = function(element) {
-  _ol_asserts_.assert(!(this.keyFunction_(element) in this.queuedElements_),
+  assert(!(this.keyFunction_(element) in this.queuedElements_),
       31); // Tried to enqueue an `element` that was already added to the queue
   var priority = this.priorityFunction_(element);
   if (priority != PriorityQueue.DROP) {
diff --git a/src/ol/style/Icon.js b/src/ol/style/Icon.js
index 0092179226..68e2dfea50 100644
--- a/src/ol/style/Icon.js
+++ b/src/ol/style/Icon.js
@@ -3,7 +3,7 @@
  */
 import {getUid, inherits} from '../index.js';
 import _ol_ImageState_ from '../ImageState.js';
-import _ol_asserts_ from '../asserts.js';
+import {assert} from '../asserts.js';
 import _ol_color_ from '../color.js';
 import _ol_events_ from '../events.js';
 import EventType from '../events/EventType.js';
@@ -80,15 +80,15 @@ var _ol_style_Icon_ = function(opt_options) {
    */
   var src = options.src;
 
-  _ol_asserts_.assert(!(src !== undefined && image),
+  assert(!(src !== undefined && image),
       4); // `image` and `src` cannot be provided at the same time
-  _ol_asserts_.assert(!image || (image && imgSize),
+  assert(!image || (image && imgSize),
       5); // `imgSize` must be set when `image` is provided
 
   if ((src === undefined || src.length === 0) && image) {
     src = image.src || getUid(image).toString();
   }
-  _ol_asserts_.assert(src !== undefined && src.length > 0,
+  assert(src !== undefined && src.length > 0,
       6); // A defined and non-empty `src` or `image` must be provided
 
   /**
diff --git a/src/ol/style/Style.js b/src/ol/style/Style.js
index 5503fe4d1c..a179d34816 100644
--- a/src/ol/style/Style.js
+++ b/src/ol/style/Style.js
@@ -1,7 +1,7 @@
 /**
  * @module ol/style/Style
  */
-import _ol_asserts_ from '../asserts.js';
+import {assert} from '../asserts.js';
 import GeometryType from '../geom/GeometryType.js';
 import _ol_style_Circle_ from '../style/Circle.js';
 import _ol_style_Fill_ from '../style/Fill.js';
@@ -291,7 +291,7 @@ _ol_style_Style_.createFunction = function(obj) {
     if (Array.isArray(obj)) {
       styles = obj;
     } else {
-      _ol_asserts_.assert(obj instanceof _ol_style_Style_,
+      assert(obj instanceof _ol_style_Style_,
           41); // Expected an `ol.style.Style` or an array of `ol.style.Style`
       styles = [obj];
     }
diff --git a/src/ol/tilegrid/TileGrid.js b/src/ol/tilegrid/TileGrid.js
index d7284c00aa..79b147eeb6 100644
--- a/src/ol/tilegrid/TileGrid.js
+++ b/src/ol/tilegrid/TileGrid.js
@@ -2,8 +2,8 @@
  * @module ol/tilegrid/TileGrid
  */
 import {DEFAULT_TILE_SIZE} from './common.js';
-import _ol_asserts_ from '../asserts.js';
-import _ol_TileRange_ from '../TileRange.js';
+import {assert} from '../asserts.js';
+import TileRange from '../TileRange.js';
 import _ol_array_ from '../array.js';
 import {createOrUpdate, getTopLeft} from '../extent.js';
 import _ol_math_ from '../math.js';
@@ -33,7 +33,7 @@ var _ol_tilegrid_TileGrid_ = function(options) {
    * @type {!Array.<number>}
    */
   this.resolutions_ = options.resolutions;
-  _ol_asserts_.assert(_ol_array_.isSorted(this.resolutions_, function(a, b) {
+  assert(_ol_array_.isSorted(this.resolutions_, function(a, b) {
     return b - a;
   }, true), 17); // `resolutions` must be sorted in descending order
 
@@ -80,7 +80,7 @@ var _ol_tilegrid_TileGrid_ = function(options) {
   this.origins_ = null;
   if (options.origins !== undefined) {
     this.origins_ = options.origins;
-    _ol_asserts_.assert(this.origins_.length == this.resolutions_.length,
+    assert(this.origins_.length == this.resolutions_.length,
         20); // Number of `origins` and `resolutions` must be equal
   }
 
@@ -91,7 +91,7 @@ var _ol_tilegrid_TileGrid_ = function(options) {
     this.origin_ = getTopLeft(extent);
   }
 
-  _ol_asserts_.assert(
+  assert(
       (!this.origin_ && this.origins_) || (this.origin_ && !this.origins_),
       18); // Either `origin` or `origins` must be configured, never both
 
@@ -102,7 +102,7 @@ var _ol_tilegrid_TileGrid_ = function(options) {
   this.tileSizes_ = null;
   if (options.tileSizes !== undefined) {
     this.tileSizes_ = options.tileSizes;
-    _ol_asserts_.assert(this.tileSizes_.length == this.resolutions_.length,
+    assert(this.tileSizes_.length == this.resolutions_.length,
         19); // Number of `tileSizes` and `resolutions` must be equal
   }
 
@@ -113,7 +113,7 @@ var _ol_tilegrid_TileGrid_ = function(options) {
   this.tileSize_ = options.tileSize !== undefined ?
     options.tileSize :
     !this.tileSizes_ ? DEFAULT_TILE_SIZE : null;
-  _ol_asserts_.assert(
+  assert(
       (!this.tileSize_ && this.tileSizes_) ||
       (this.tileSize_ && !this.tileSizes_),
       22); // Either `tileSize` or `tileSizes` must be configured, never both
@@ -139,7 +139,7 @@ var _ol_tilegrid_TileGrid_ = function(options) {
 
   if (options.sizes !== undefined) {
     this.fullTileRanges_ = options.sizes.map(function(size, z) {
-      var tileRange = new _ol_TileRange_(
+      var tileRange = new TileRange(
           Math.min(0, size[0]), Math.max(size[0] - 1, -1),
           Math.min(0, size[1]), Math.max(size[1] - 1, -1));
       return tileRange;
@@ -199,7 +199,7 @@ _ol_tilegrid_TileGrid_.prototype.forEachTileCoordParentTileRange = function(tile
     if (this.zoomFactor_ === 2) {
       x = Math.floor(x / 2);
       y = Math.floor(y / 2);
-      tileRange = _ol_TileRange_.createOrUpdate(x, x, y, y, opt_tileRange);
+      tileRange = TileRange.createOrUpdate(x, x, y, y, opt_tileRange);
     } else {
       tileRange = this.getTileRangeForExtentAndZ(tileCoordExtent, z, opt_tileRange);
     }
@@ -288,7 +288,7 @@ _ol_tilegrid_TileGrid_.prototype.getTileCoordChildTileRange = function(tileCoord
     if (this.zoomFactor_ === 2) {
       var minX = tileCoord[1] * 2;
       var minY = tileCoord[2] * 2;
-      return _ol_TileRange_.createOrUpdate(minX, minX + 1, minY, minY + 1, opt_tileRange);
+      return TileRange.createOrUpdate(minX, minX + 1, minY, minY + 1, opt_tileRange);
     }
     var tileCoordExtent = this.getTileCoordExtent(tileCoord, opt_extent);
     return this.getTileRangeForExtentAndZ(
@@ -330,7 +330,7 @@ _ol_tilegrid_TileGrid_.prototype.getTileRangeForExtentAndZ = function(extent, z,
   var minX = tileCoord[1];
   var minY = tileCoord[2];
   this.getTileCoordForXYAndZ_(extent[2], extent[3], z, true, tileCoord);
-  return _ol_TileRange_.createOrUpdate(
+  return TileRange.createOrUpdate(
       minX, tileCoord[1], minY, tileCoord[2], opt_tileRange);
 };
 
diff --git a/src/ol/tileurlfunction.js b/src/ol/tileurlfunction.js
index a5fd27d156..29732c99be 100644
--- a/src/ol/tileurlfunction.js
+++ b/src/ol/tileurlfunction.js
@@ -1,7 +1,7 @@
 /**
  * @module ol/tileurlfunction
  */
-import _ol_asserts_ from './asserts.js';
+import {assert} from './asserts.js';
 import _ol_math_ from './math.js';
 import _ol_tilecoord_ from './tilecoord.js';
 
@@ -36,7 +36,7 @@ export function createFromTemplate(template, tileGrid) {
             .replace(dashYRegEx, function() {
               var z = tileCoord[0];
               var range = tileGrid.getFullTileRange(z);
-              _ol_asserts_.assert(range, 55); // The {-y} placeholder requires a tile grid with extent
+              assert(range, 55); // The {-y} placeholder requires a tile grid with extent
               var y = range.getHeight() + tileCoord[2];
               return y.toString();
             });
diff --git a/src/ol/transform.js b/src/ol/transform.js
index 54dbb3d9b9..e85bc7b332 100644
--- a/src/ol/transform.js
+++ b/src/ol/transform.js
@@ -1,7 +1,7 @@
 /**
  * @module ol/transform
  */
-import _ol_asserts_ from './asserts.js';
+import {assert} from './asserts.js';
 var _ol_transform_ = {};
 
 
@@ -204,7 +204,7 @@ _ol_transform_.compose = function(transform, dx1, dy1, sx, sy, angle, dx2, dy2)
  */
 _ol_transform_.invert = function(transform) {
   var det = _ol_transform_.determinant(transform);
-  _ol_asserts_.assert(det !== 0, 32); // Transformation matrix cannot be inverted
+  assert(det !== 0, 32); // Transformation matrix cannot be inverted
 
   var a = transform[0];
   var b = transform[1];
diff --git a/test/spec/ol/asserts.test.js b/test/spec/ol/asserts.test.js
index 5129141401..3797fd7ce6 100644
--- a/test/spec/ol/asserts.test.js
+++ b/test/spec/ol/asserts.test.js
@@ -1,4 +1,4 @@
-import _ol_asserts_ from '../../../src/ol/asserts.js';
+import {assert} from '../../../src/ol/asserts.js';
 
 
 describe('ol.asserts', function() {
@@ -6,7 +6,7 @@ describe('ol.asserts', function() {
   describe('ol.asserts.assert', function() {
     it('throws an exception', function() {
       expect(function() {
-        _ol_asserts_.assert(false, 42);
+        assert(false, 42);
       }).to.throwException();
     });
   });
diff --git a/test/spec/ol/featureloader.test.js b/test/spec/ol/featureloader.test.js
index 6165a735d6..6865ef1ef3 100644
--- a/test/spec/ol/featureloader.test.js
+++ b/test/spec/ol/featureloader.test.js
@@ -1,4 +1,4 @@
-import _ol_featureloader_ from '../../../src/ol/featureloader.js';
+import {xhr} from '../../../src/ol/featureloader.js';
 import GeoJSON from '../../../src/ol/format/GeoJSON.js';
 import _ol_source_Vector_ from '../../../src/ol/source/Vector.js';
 
@@ -19,7 +19,7 @@ describe('ol.featureloader', function() {
     });
 
     it('adds features to the source', function(done) {
-      loader = _ol_featureloader_.xhr(url, format);
+      loader = xhr(url, format);
       source.on('addfeature', function(e) {
         expect(source.getFeatures().length).to.be.greaterThan(0);
         done();
@@ -32,7 +32,7 @@ describe('ol.featureloader', function() {
         url = function(extent, resolution, projection) {
           return 'spec/ol/data/point.json';
         };
-        loader = _ol_featureloader_.xhr(url, format);
+        loader = xhr(url, format);
 
         source.on('addfeature', function(e) {
           expect(source.getFeatures().length).to.be.greaterThan(0);
@@ -52,7 +52,7 @@ describe('ol.featureloader', function() {
           done();
           return 'spec/ol/data/point.json';
         };
-        loader = _ol_featureloader_.xhr(url, format);
+        loader = xhr(url, format);
         loader.call(source, [], 1, 'EPSG:3857');
       });
     });
diff --git a/test/spec/ol/source/tile.test.js b/test/spec/ol/source/tile.test.js
index 9bc8a121ab..1bdb607e5d 100644
--- a/test/spec/ol/source/tile.test.js
+++ b/test/spec/ol/source/tile.test.js
@@ -1,6 +1,6 @@
 import {inherits} from '../../../../src/ol/index.js';
 import _ol_Tile_ from '../../../../src/ol/Tile.js';
-import _ol_TileRange_ from '../../../../src/ol/TileRange.js';
+import TileRange from '../../../../src/ol/TileRange.js';
 import {get as getProjection} from '../../../../src/ol/proj.js';
 import _ol_proj_Projection_ from '../../../../src/ol/proj/Projection.js';
 import _ol_source_Source_ from '../../../../src/ol/source/Source.js';
@@ -154,7 +154,7 @@ describe('ol.source.Tile', function() {
       });
 
       var zoom = 1;
-      var range = new _ol_TileRange_(0, 1, 0, 1);
+      var range = new TileRange(0, 1, 0, 1);
 
       source.forEachLoadedTile(source.getProjection(), zoom, range, callback);
       expect(callback.callCount).to.be(3);
@@ -170,7 +170,7 @@ describe('ol.source.Tile', function() {
       });
 
       var zoom = 1;
-      var range = new _ol_TileRange_(0, 1, 0, 1);
+      var range = new TileRange(0, 1, 0, 1);
 
       var covered = source.forEachLoadedTile(
           source.getProjection(), zoom, range,
@@ -190,7 +190,7 @@ describe('ol.source.Tile', function() {
       });
 
       var zoom = 1;
-      var range = new _ol_TileRange_(0, 1, 0, 1);
+      var range = new TileRange(0, 1, 0, 1);
 
       var covered = source.forEachLoadedTile(
           source.getProjection(), zoom,
@@ -210,7 +210,7 @@ describe('ol.source.Tile', function() {
       });
 
       var zoom = 1;
-      var range = new _ol_TileRange_(0, 1, 0, 1);
+      var range = new TileRange(0, 1, 0, 1);
 
       var covered = source.forEachLoadedTile(
           source.getProjection(), zoom, range,
diff --git a/test/spec/ol/tilegrid/tilegrid.test.js b/test/spec/ol/tilegrid/tilegrid.test.js
index 1d1c4e9b2b..6f71131daf 100644
--- a/test/spec/ol/tilegrid/tilegrid.test.js
+++ b/test/spec/ol/tilegrid/tilegrid.test.js
@@ -1,5 +1,5 @@
 import {DEFAULT_MAX_ZOOM, DEFAULT_TILE_SIZE} from '../../../../src/ol/tilegrid/common.js';
-import _ol_TileRange_ from '../../../../src/ol/TileRange.js';
+import TileRange from '../../../../src/ol/TileRange.js';
 import * as _ol_extent_ from '../../../../src/ol/extent.js';
 import {get as getProjection, METERS_PER_UNIT} from '../../../../src/ol/proj.js';
 import _ol_proj_EPSG3857_ from '../../../../src/ol/proj/EPSG3857.js';
@@ -504,7 +504,7 @@ describe('ol.tilegrid.TileGrid', function() {
           tileCoord,
           function(z, tileRange) {
             zs.push(z);
-            tileRanges.push(new _ol_TileRange_(
+            tileRanges.push(new TileRange(
                 tileRange.minX, tileRange.maxX,
                 tileRange.minY, tileRange.maxY));
             return false;
diff --git a/test/spec/ol/tilerange.test.js b/test/spec/ol/tilerange.test.js
index 81a4748871..ac5f3716ec 100644
--- a/test/spec/ol/tilerange.test.js
+++ b/test/spec/ol/tilerange.test.js
@@ -1,17 +1,17 @@
-import _ol_TileRange_ from '../../../src/ol/TileRange.js';
+import TileRange from '../../../src/ol/TileRange.js';
 
 
 describe('ol.TileRange', function() {
 
   describe('constructor', function() {
     it('creates a range', function() {
-      var range = new _ol_TileRange_(1, 3, 2, 4);
-      expect(range).to.be.a(_ol_TileRange_);
+      var range = new TileRange(1, 3, 2, 4);
+      expect(range).to.be.a(TileRange);
     });
 
     it('can represent a range of one tile', function() {
-      var range = new _ol_TileRange_(2, 2, 3, 3);
-      expect(range).to.be.a(_ol_TileRange_);
+      var range = new TileRange(2, 2, 3, 3);
+      expect(range).to.be.a(TileRange);
       expect(range.getHeight()).to.be(1);
       expect(range.getWidth()).to.be(1);
     });
@@ -19,7 +19,7 @@ describe('ol.TileRange', function() {
 
   describe('contains', function() {
     it('returns the expected value', function() {
-      var tileRange = new _ol_TileRange_(1, 3, 1, 3);
+      var tileRange = new TileRange(1, 3, 1, 3);
       expect(tileRange.contains([0, 0, 0])).to.not.be();
       expect(tileRange.contains([0, 0, 1])).to.not.be();
       expect(tileRange.contains([0, 0, 2])).to.not.be();
@@ -50,12 +50,12 @@ describe('ol.TileRange', function() {
 
   describe('equals', function() {
     it('determines equivalence of two ranges', function() {
-      var one = new _ol_TileRange_(0, 2, 1, 4);
-      var same = new _ol_TileRange_(0, 2, 1, 4);
-      var diff1 = new _ol_TileRange_(0, 2, 1, 5);
-      var diff2 = new _ol_TileRange_(0, 3, 1, 4);
-      var diff3 = new _ol_TileRange_(0, 2, 2, 4);
-      var diff4 = new _ol_TileRange_(1, 2, 1, 4);
+      var one = new TileRange(0, 2, 1, 4);
+      var same = new TileRange(0, 2, 1, 4);
+      var diff1 = new TileRange(0, 2, 1, 5);
+      var diff2 = new TileRange(0, 3, 1, 4);
+      var diff3 = new TileRange(0, 2, 2, 4);
+      var diff4 = new TileRange(1, 2, 1, 4);
       expect(one.equals(same)).to.be(true);
       expect(one.equals(diff1)).to.be(false);
       expect(one.equals(diff2)).to.be(false);
@@ -66,8 +66,8 @@ describe('ol.TileRange', function() {
 
   describe('extent', function() {
     it('modifies range so it includes another', function() {
-      var one = new _ol_TileRange_(0, 2, 1, 4);
-      var other = new _ol_TileRange_(-1, -3, 10, 12);
+      var one = new TileRange(0, 2, 1, 4);
+      var other = new TileRange(-1, -3, 10, 12);
       one.extend(other);
 
       expect(one.minX).to.be(-1);
@@ -80,7 +80,7 @@ describe('ol.TileRange', function() {
 
   describe('getSize', function() {
     it('returns the expected size', function() {
-      var tileRange = new _ol_TileRange_(0, 2, 1, 4);
+      var tileRange = new TileRange(0, 2, 1, 4);
       var size = tileRange.getSize();
       expect(size).to.eql([3, 4]);
     });
@@ -88,20 +88,20 @@ describe('ol.TileRange', function() {
 
   describe('intersects', function() {
     it('determines if two ranges overlap', function() {
-      var one = new _ol_TileRange_(0, 2, 1, 4);
-      var overlapsRight = new _ol_TileRange_(2, 4, 1, 4);
-      var overlapsLeft = new _ol_TileRange_(-3, 0, 1, 4);
-      var overlapsTop = new _ol_TileRange_(0, 2, 4, 5);
-      var overlapsBottom = new _ol_TileRange_(0, 2, -3, 1);
+      var one = new TileRange(0, 2, 1, 4);
+      var overlapsRight = new TileRange(2, 4, 1, 4);
+      var overlapsLeft = new TileRange(-3, 0, 1, 4);
+      var overlapsTop = new TileRange(0, 2, 4, 5);
+      var overlapsBottom = new TileRange(0, 2, -3, 1);
       expect(one.intersects(overlapsLeft)).to.be(true);
       expect(one.intersects(overlapsRight)).to.be(true);
       expect(one.intersects(overlapsTop)).to.be(true);
       expect(one.intersects(overlapsBottom)).to.be(true);
 
-      var right = new _ol_TileRange_(3, 5, 1, 4);
-      var left = new _ol_TileRange_(-3, -1, 1, 4);
-      var above = new _ol_TileRange_(0, 2, 5, 6);
-      var below = new _ol_TileRange_(0, 2, -3, 0);
+      var right = new TileRange(3, 5, 1, 4);
+      var left = new TileRange(-3, -1, 1, 4);
+      var above = new TileRange(0, 2, 5, 6);
+      var below = new TileRange(0, 2, -3, 0);
       expect(one.intersects(right)).to.be(false);
       expect(one.intersects(left)).to.be(false);
       expect(one.intersects(above)).to.be(false);