How to write an asynchronous JavaScript method?

Question

I have been working on async programming in JavaScript recently. I've been coming through many code snippets and also in jQuery methods, where if we pass a callback function as a parameter to another function, it executes asynchronously. The call back is executed after the execution of that function completes.

I have been through some answers on Stack Exchange network on this topic. One guy said we cannot make our code asynchronous unless we depend on a native method for that functionality

see here https://stackoverflow.com/a/9516967

alse here https://softwareengineering.stackexchange.com/a/194591

Another guy said that just passing callbacks to events makes our code asynchronous. https://softwareengineering.stackexchange.com/a/194581

My question is that what makes code asynchronous, by just passing a callback, or should we depend on native methods like setTimeout or setInterval to attain async functionality?

You can't achieve asynchronous javascript by setTimeout or setInterval. That simply goes against the meaning of "real" asynchronous. Timers can't be asynchronous as they depend on so much thing. Though if I continue my monolog, I think I will come to the point where nothing is "real" asynchronous in computer (ofcourse if we don't consider that code can run on multiple threads or even multiple cores) :) — Arman P.
– Arman P., Commented Feb 7, 2014 at 5:25
the easiest method is to create a timer as you have stated. This still requires the client to continue running your code or the async code will stop executing...Server side RESTful calls would allow you to make a rest call (async run on server) then get a callback this question however is architecture in nature and thereby this isn't the right forum for it. — abc123
– abc123, Commented Feb 7, 2014 at 5:27

andyf · Accepted Answer · 2014-02-07 05:35:48Z

1

Asynchronous means JavaScript is non-blocking when handling I/O.

Here is a sample from Node.js in Action:

  $.post('/resource.json', function (data) { // I/O does not block execution
      console.log(data);
  });

Notice that the code was NOT written like this:

 var data = $.post('/resource.json');
 console.log(data);

answered Feb 7, 2014 at 5:35

andyf

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