I hope that when using asynchronous callback method, I can use the structure more clearly to syntax a synchronous call. It means I can use indentation to show block-level relationships and logic. Although future browsers will all build in the "Promise" to support the asynchronous callback. But currently only chrome and firefox support it, so I have to make a js library like Promise mechanism. Then it can work on all browsers.  Proimse Compatibility Notes:  https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise#Browser_compatibility