Add a concat function for concatenating strings

src/ol/expr/expression.js

@@ -95,6 +95,7 @@ ol.expr.lib = {};
  * @enum {string}
  */
 ol.expr.functions = {
+  CONCAT: 'concat',
   EXTENT: 'extent',
   FID: 'fid',
   GEOMETRY_TYPE: 'geometryType',
@@ -108,6 +109,22 @@ ol.expr.functions = {
 };
 
 
+/**
+ * Concatenate strings.  All provided arguments will be cast to string and
+ * concatenated.
+ * @param {...string} var_args Strings to concatenate.
+ * @return {string} All input arguments concatenated as strings.
+ * @this {ol.Feature}
+ */
+ol.expr.lib[ol.expr.functions.CONCAT] = function(var_args) {
+  var str = '';
+  for (var i = 0, ii = arguments.length; i < ii; ++i) {
+    str += String(arguments[i]);
+  }
+  return str;
+};
+
+
 /**
  * Determine if a feature's extent intersects the provided extent.
  * @param {number} minX Minimum x-coordinate value.

test/spec/ol/expr/expression.test.js

@@ -628,6 +628,52 @@ describe('ol.expr.lib', function() {
   var parse = ol.expr.parse;
   var evaluate = ol.expr.evaluateFeature;
 
+  describe('concat()', function() {
+    var feature = new ol.Feature({
+      str: 'bar',
+      num: 42,
+      bool: false,
+      nul: null
+    });
+
+    it('concatenates strings', function() {
+      expect(evaluate(parse('concat(str, "after")'), feature))
+          .to.be('barafter');
+      expect(evaluate(parse('concat("before", str)'), feature))
+          .to.be('beforebar');
+      expect(evaluate(parse('concat("a", str, "b")'), feature))
+          .to.be('abarb');
+    });
+
+    it('concatenates numbers as strings', function() {
+      expect(evaluate(parse('concat(num, 0)'), feature))
+          .to.be('420');
+      expect(evaluate(parse('concat(0, num)'), feature))
+          .to.be('042');
+      expect(evaluate(parse('concat(42, 42)'), feature))
+          .to.be('4242');
+      expect(evaluate(parse('concat(str, num)'), feature))
+          .to.be('bar42');
+    });
+
+    it('concatenates booleans as strings', function() {
+      expect(evaluate(parse('concat(bool, "foo")'), feature))
+          .to.be('falsefoo');
+      expect(evaluate(parse('concat(true, str)'), feature))
+          .to.be('truebar');
+      expect(evaluate(parse('concat(true, false)'), feature))
+          .to.be('truefalse');
+    });
+
+    it('concatenates nulls as strings', function() {
+      expect(evaluate(parse('concat(nul, "foo")'), feature))
+          .to.be('nullfoo');
+      expect(evaluate(parse('concat(str, null)'), feature))
+          .to.be('barnull');
+    });
+
+  });
+
   describe('extent()', function() {
 
     var nw = new ol.Feature({