Sleep in JavaScript - delay between actions

In case you really need a sleep() just to test something. But be aware that it'll crash the browser most of the times while debuggin - probably that's why you need it anyway. In production mode I'll comment out this function.

function pauseBrowser(millis) {
    var date = Date.now();
    var curDate = null;
    do {
        curDate = Date.now();
    } while (curDate-date < millis);
}

Don't use new Date() in the loop, unless you want to waste memory, processing power, battery and possibly the lifetime of your device.

You can use setTimeout to achieve a similar effect:

var a = 1 + 3;
var b;
setTimeout(function() {
    b = a + 4;
}, (3 * 1000));

This doesn't really 'sleep' JavaScript—it just executes the function passed to setTimeout after a certain duration (specified in milliseconds). Although it is possible to write a sleep function for JavaScript, it's best to use setTimeout if possible as it doesn't freeze everything during the sleep period.