fix #127 ensure callback called once even if it throws

index.js

@@ -51,11 +51,18 @@ function createXHR(uri, options, callback) {
 }
 
 function _createXHR(options) {
-    var callback = options.callback
-    if(typeof callback === "undefined"){
+    if(typeof options.callback === "undefined"){
         throw new Error("callback argument missing")
     }
 
+    var called = false
+    var callback = function cbOnce(err, response, body){
+        if(!called){
+            called = true
+            options.callback(err, response, body)
+        }
+    }
+
     function readystatechange() {
         if (xhr.readyState === 4) {
             loadFunc()
@@ -96,8 +103,7 @@ function _createXHR(options) {
             evt = new Error("" + (evt || "Unknown XMLHttpRequest Error") )
         }
         evt.statusCode = 0
-        callback(evt, failureResponse)
-        callback = noop
+        return callback(evt, failureResponse)
     }
 
     // will load the data & process the response in a special response object
@@ -129,9 +135,7 @@ function _createXHR(options) {
         } else {
             err = new Error("Internal XMLHttpRequest Error")
         }
-        callback(err, response, response.body)
-        callback = noop
-
+        return callback(err, response, response.body)
     }
 
     var xhr = options.xhr || null

test/index.js

@@ -52,6 +52,22 @@ test("[func] Returns a falsy body for 204 responses", function(assert) {
     })
 })
 
+test("[func] Calls the callback once even if error is thrown issue #127", function(assert) {
+    var count = 0;
+    setTimeout(function(){
+        assert.equal(count, 1, "expected one call")
+        assert.end()
+    },100)
+    try{
+        xhr({
+            uri: "instanterror://foo"
+        }, function(err, resp, body) {
+            count++;
+            throw Error("dummy error")
+        })
+    } catch(e){}
+})
+
 test("[func] Times out to an error ", function(assert) {
     xhr({
         timeout: 1,