What is a simple example of an asynchronous javascript function? [closed]

Answer 1

Here's one very simple example:

for (var i = 0; i < 10; i++) {
  window.setTimeout(function() {
    console.log(i);
  }, 2000);
}

You might expect these console.log() calls to show you 0, 1, 2 etc., as in this snippet:

for (var i = 0; i < 10; i++) {
  console.log(i);
}

But in fact only 10s will be printed! The reason that functions passed into setTimeout function (as its 'callback' argument) will be invoked after for loop is completed - i.e., after i value is set to 10.

Yet you should understood one thing: all JavaScript in a browser executes on a single thread; asynchronous events (such as mouse clicks and timers) are only run when there's been an opening in the execution queue. Here's a brilliant article written by John Resig on this topic.