Only use the alt text of image elements as a fallback

NEWS

@@ -1,3 +1,9 @@
+# 1.5.0
+
+* Only use the alt text of image elements as a fallback. If an alt attribute is
+  returned from the function passed to mammoth.images.imgElement, that value
+  will now be preferred to the alt text of the image element.
+
 # 1.4.21
 
 * Ignore w:u elements when w:val is missing.

lib/images.js

@@ -8,10 +8,12 @@ exports.imgElement = imgElement;
 function imgElement(func) {
     return function(element, messages) {
         return promises.when(func(element)).then(function(result) {
-            var attributes = _.clone(result);
+            var attributes = {};
             if (element.altText) {
                 attributes.alt = element.altText;
             }
+            _.extend(attributes, result);
+
             return [Html.freshElement("img", attributes)];
         });
     };

test/images.tests.js

@@ -83,5 +83,30 @@ test('mammoth.images.imgElement()', {
                 })
             ));
         });
+    },
+
+    'image alt text can be overriden by alt attribute returned from function': function() {
+        var imageBuffer = new Buffer("abc");
+        var image = new documents.Image({
+            readImage: function(encoding) {
+                return promises.when(imageBuffer.toString(encoding));
+            },
+            contentType: "image/jpeg",
+            altText: "<alt>"
+        });
+
+        var result = mammoth.images.imgElement(function(image) {
+            return {alt: "<alt override>", src: "<src>"};
+        })(image);
+
+        return result.then(function(result) {
+            assertThat(result, contains(
+                hasProperties({
+                    tag: hasProperties({
+                        attributes: equalTo({alt: "<alt override>", src: "<src>"})
+                    })
+                })
+            ));
+        });
     }
 });