Fix #12803. Add jQuery.fx.start as a hook point. Close gh-1024.

src/effects.js

@@ -640,13 +640,19 @@ jQuery.fx.tick = function() {
 };
 
 jQuery.fx.timer = function( timer ) {
-	if ( timer() && jQuery.timers.push( timer ) && !timerId ) {
-		timerId = setInterval( jQuery.fx.tick, jQuery.fx.interval );
+	if ( timer() && jQuery.timers.push( timer ) ) {
+		jQuery.fx.start();
 	}
 };
 
 jQuery.fx.interval = 13;
 
+jQuery.fx.start = function() {
+	if ( !timerId ) {
+		timerId = setInterval( jQuery.fx.tick, jQuery.fx.interval );
+	}
+};
+
 jQuery.fx.stop = function() {
 	clearInterval( timerId );
 	timerId = null;

test/unit/effects.js

@@ -1877,4 +1877,31 @@ jQuery.map([ "toggle", "slideToggle", "fadeToggle" ], function ( method ) {
 	});
 });
 
+test( "jQuery.fx.start & jQuery.fx.stop hook points", function() {
+	var oldStart = jQuery.fx.start,
+		oldStop = jQuery.fx.stop,
+		foo = jQuery({ foo: 0 });
+
+	expect( 3 );
+
+	jQuery.fx.start = function() {
+		ok( true, "start called" );
+	};
+	jQuery.fx.stop = function() {
+		ok( true, "stop called" );
+	};
+
+	// calls start
+	foo.animate({ foo: 1 }, { queue: false });
+	// calls start
+	foo.animate({ foo: 2 }, { queue: false });
+	foo.stop();
+	// calls stop
+	jQuery.fx.tick();
+
+	// cleanup
+	jQuery.fx.start = oldStart;
+	jQuery.fx.stop = oldStop;
+});
+
 } // if ( jQuery.fx )