Updated

master/examples/export-jpeg.js

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+var map = new ol.Map({
+  layers: [
+    new ol.layer.TileLayer({
+      source: new ol.source.OpenStreetMap()
+    })
+  ],
+  renderer: ol.RendererHint.CANVAS,
+  target: 'map',
+  view: new ol.View2D({
+    center: new ol.Coordinate(0, 0),
+    zoom: 2
+  })
+});
+
+var exportJPEGElement = document.getElementById('export-jpeg');
+exportJPEGElement.addEventListener('click', function(e) {
+  e.target.href = map.getRenderer().getCanvas().toDataURL('image/jpeg');
+}, false);