Add support for proper onprogress events for file uploads

README.md

@@ -71,6 +71,7 @@ Parameters:
     + string (sets content type to 'application/x-www-form-urlencoded' if not set in headers)
     + FormData (doesn't set content type so that browser will set as appropriate)
 - `method`: 'GET', 'POST', etc. Defaults to 'GET' or 'POST' based on body
+- `onprogress`: function callback, will be called multiple times with a progress event when uploading files using FormData
 - `cors`: If your using cross-origin, you will need this true for IE8-9 (to use the XDomainRequest object, also see [Compatibility](#compatibility))
 
 The following parameters are passed directly onto the request object:

index.js

@@ -81,8 +81,13 @@ exports.ajax = function (params, callback) {
 
   for (var i = 0, len = reqfields.length, field; i < len; i++) {
     field = reqfields[i]
-    if (params[field] !== undefined)
-      req[field] = params[field]
+    if (params[field] !== undefined){
+      if(body && global.FormData && body instanceof global.FormData && field == 'onprogress'){
+        req.upload[field] = params[field];
+      }else{
+        req[field] = params[field];
+      }
+    }
   }
 
   for (var field in headers)

test/index.js

@@ -100,6 +100,28 @@ function defineTests(ajax) {
           done()
         })
       })
+
+      test('FormData progress', function(done){
+        var formData = new FormData();
+        formData.append("arg", "value");
+        formData.append("foo", "bar");
+
+        var isLengthComputable = false;
+
+        var progressHandler = function(e){
+          isLengthComputable = e.lengthComputable;
+        }
+
+        ajax({url: '/post',
+              body: formData,
+              method: 'POST',
+              onprogress: progressHandler
+        }, function (code, body) {
+          assert.equal(isLengthComputable, true)
+          done()
+        })
+
+      })
     }
 
     // Safari: