Add some comments.

Author: octalmage

.gitignore

@@ -1,3 +1,4 @@
 vendor/
 node_modules/
 build/
+phpcompat.zip

src/js/run.js

@@ -76,6 +76,8 @@ function checkStatus() {
 
 	var obj;
 	jQuery.post( ajaxurl, data, function( obj ) {
+		// TODO: Without jQuery migrate an empty response can throw a JSON parse error.
+		// So we should do the parsing manually.
 		if ( !obj ) {
 			startTimer();
 			return;

tests/qunit/index.html

@@ -11,6 +11,7 @@
 	<div id="qunit-fixture"></div>
 	<script src="https://code.jquery.com/qunit/qunit-2.0.0.js"></script>
 	<script src="https://code.jquery.com/jquery-1.12.4.min.js"></script>
+	<script src="https://code.jquery.com/jquery-migrate-1.4.1.js"></script>
 	<script src="https://code.jquery.com/ui/1.11.4/jquery-ui.js"></script>
 	<script src="https://cdn.jsdelivr.net/jquery.mockjax/2.2.0/jquery.mockjax.min.js"></script>
 	<script src="../../src/js/handlebars.js"></script>

tests/qunit/test-run.js

@@ -148,6 +148,7 @@ QUnit.test( 'Test checkStatus done', function( assert ) {
 	checkStatus();
 });
 
+// This happens when the test doesn't start before checkStatus is called.
 QUnit.test( 'Test checkStatus empty result', function( assert ) {
 	var done = assert.async();
 	var fixture = $( '#qunit-fixture' );