Support Promise style instead of passing a callback

Author: yusitnikov

README.md

@@ -11,13 +11,14 @@ The library contains only one script `fix-webm-duration.js` and has no dependenc
 Syntax:
 
 ```javascript
-ysFixWebmDuration(blob, duration, callback, options = {});
+ysFixWebmDuration(blob, duration, callback = undefined, options = {});
 ```
 
 where
 - `blob` is `Blob` object with file contents from `MediaRecorder`
 - `duration` is video duration in milliseconds (you should calculate it while recording the video)
-- `callback` is callback function that will receive fixed blob
+- `callback` is callback function that will receive fixed blob.
+  If omitted, a `Promise` object will be returned instead.
 - `options` is an object of options:
   - `options.logger` - a callback for logging debug messages or `false`.
     The callback should accept one argument - the message string.
@@ -41,10 +42,17 @@ function startRecording(stream, options) {
     mediaRecorder.onstop = function() {
         var duration = Date.now() - startTime;
         var buggyBlob = new Blob(mediaParts, { type: 'video/webm' });
-        
+
+        // v1: callback-style
         ysFixWebmDuration(buggyBlob, duration, function(fixedBlob) {
             displayResult(fixedBlob);
         });
+
+        // v2: promise-style, disable logging
+        ysFixWebmDuration(buggyBlob, duration, {logger: false})
+            .then(function(fixedBlob) {
+                displayResult(fixedBlob);
+            });
     };
     mediaRecorder.ondataavailable = function(event) {
         var data = event.data;

fix-webm-duration.js

@@ -474,7 +474,19 @@
         return new Blob([ this.source.buffer ], { type: 'video/webm' });
     };
 
-    return function(blob, duration, callback, options) {
+    function fixWebmDuration(blob, duration, callback, options) {
+        // The callback may be omitted - then the third argument is options
+        if (typeof callback === "object") {
+            options = callback;
+            callback = undefined;
+        }
+
+        if (!callback) {
+            return new Promise(function(resolve) {
+                fixWebmDuration(blob, duration, resolve, options);
+            });
+        }
+
         try {
             var reader = new FileReader();
             reader.onloadend = function() {
@@ -492,5 +504,7 @@
         } catch (ex) {
             callback(blob);
         }
-    };
+    }
+
+    return fixWebmDuration;
 });