28 April, 2009


2009/08/23 Update:
This is only really useful if you need to do asynchronous calls 11 or more times. If you only need to make a few calls, it would be better to just use the (function () {}()); construct.

Here is a new function I have recently created:

"use strict";
var waitUntil = function anon(func, ms) {
    ms = ms || 100;
    if (func() !== true) {
        return setTimeout(function () {
            anon(func, ms);
        }, ms);

I don't know about you, but in my code I have to frequently test a condition... but do so asynchronously. You can do this with setTimeout, but it requires a lot of syntax and work to get it right. The above function attempts to ease this a little.

You call it like so:

waitUntil(function () {
    if (test === 5) {
        return true;
This is the same as if I had done:
(function anon() {
    if (test === 5) {
    } else {
        setTimeout(anon, 100);

Not a huge difference, but still useful when you need to perform such checks on a regular basis. waitUntil accepts two arguments:

  1. This should be a function. waitUntil will continue executing this function until it returns true, which tells waitUntil to stop.
  2. This should be a number. This is how often waitUntil will run the function, in milliseconds. The default is 100.

In addition, waitUntil returns a setTimeout, so you can use clearTimeout to halt the check at any time:

var timer = waitUntil(function () {
    if (test === 5) {
        return true;
}, 300);

[LINK] The unit tests.

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