fix respond() & readystatechange process flow (#184)

* codejedi365-fix-readystatechange-flow > add test

### Rationale
Added issue replication test for issue #165 where readystatechange
event is occuring after loadend event occurs.

* codejedi365-fix-readystatechange-flow > resolved

### Rationale
The code was using fall through logic which caused the extra
readystatechange event to be thrown after the loadend event.  The logic
was there to delinate from a finished XHR request and throw the loadend
but not to stop processing. Note that a readystatechange did have to be
added prior to the loadend otherwise some requests would not resolve
and it was noticeable through other unit-tests. This commit has all
passing tests to include the one designed to replicate the issue of

Resolves #165

* codejedi365-fix-readystatechange-flow > improve codestyle

### Rationale
Ensure logic is clear by avoiding empty return statements and fall-through logic

lib/fake-xhr/index.js

@@ -513,8 +513,6 @@ function fakeXMLHttpRequestFor(globalScope) {
                 false,
                 this
             );
-            var event, progress;
-
             if (typeof this.onreadystatechange === "function") {
                 try {
                     this.onreadystatechange(readyStateChangeEvent);
@@ -523,7 +521,11 @@ function fakeXMLHttpRequestFor(globalScope) {
                 }
             }
 
-            if (this.readyState === FakeXMLHttpRequest.DONE) {
+            if (this.readyState !== FakeXMLHttpRequest.DONE) {
+                this.dispatchEvent(readyStateChangeEvent);
+            } else {
+                var event, progress;
+
                 if (this.timedOut || this.aborted || this.status === 0) {
                     progress = { loaded: 0, total: 0 };
                     event =
@@ -553,12 +555,11 @@ function fakeXMLHttpRequestFor(globalScope) {
                 this.dispatchEvent(
                     new sinonEvent.ProgressEvent(event, progress, this)
                 );
+                this.dispatchEvent(readyStateChangeEvent);
                 this.dispatchEvent(
                     new sinonEvent.ProgressEvent("loadend", progress, this)
                 );
             }
-
-            this.dispatchEvent(readyStateChangeEvent);
         },
 
         // Ref https://xhr.spec.whatwg.org/#the-setrequestheader()-method

lib/fake-xhr/index.test.js

@@ -1212,6 +1212,29 @@ describe("FakeXMLHttpRequest", function() {
             assert.equals(status, 204);
             assert.equals(statusText, "No Content");
         });
+
+        it("only performs readystatechange events prior to loadend event during xhr response", function() {
+            var eventLog = [];
+            this.xhr.addEventListener("readystatechange", function() {
+                eventLog.push({
+                    event: "readystatechange",
+                    timestamp: Date.now()
+                });
+            });
+            this.xhr.addEventListener("loadend", function() {
+                eventLog.push({ event: "loadend", timestamp: Date.now() });
+            });
+            this.xhr.respond(200);
+
+            // Loadend is last event
+            assert.equals(eventLog[eventLog.length - 1].event, "loadend");
+            // Only 1 loadend event occurs
+            assert.equals(
+                eventLog.filter(item => item.event !== "readystatechange")
+                    .length,
+                1
+            );
+        });
     });
 
     describe(".getResponseHeader", function() {