What is the JavaScript version of sleep()?

Question

Is there a better way to engineer a sleep in JavaScript than the following pausecomp function (taken from here)?

function pausecomp(millis)
{
    var date = new Date();
    var curDate = null;
    do { curDate = new Date(); }
    while(curDate-date < millis);
}

This is not a duplicate of Sleep in JavaScript - delay between actions; I want a real sleep in the middle of a function, and not a delay before a piece of code executes.

Answer 1

2017 — 2019 update

Since 2009 when this question was asked, JavaScript has evolved significantly. All other answers are now obsolete or overly complicated. Here is the current best practice:

function sleep(ms) {
  return new Promise(resolve => setTimeout(resolve, ms));
}

async function demo() {
  console.log('Taking a break...');
  await sleep(2000);
  console.log('Two seconds later, showing sleep in a loop...');

  // Sleep in loop
  for (let i = 0; i < 5; i++) {
    if (i === 3)
      await sleep(2000);
    console.log(i);
  }
}

demo();

This is it. await sleep(<duration>).

Or as a one-liner:

await new Promise(r => setTimeout(r, 2000));

Note that,

1. await can only be executed in functions prefixed with the async keyword, or at the top level of your script in some environments (e.g. the Chrome DevTools console, or Runkit).
2. await only pauses the current async function

Two new JavaScript features helped write this "sleep" function:

• Promises, a native feature of ES2015 (aka ES6). We also use arrow functions in the definition of the sleep function.
• The async/await feature lets the code explicitly wait for a promise to settle (resolve or reject).

Compatibility

• promises are supported in Node v0.12+ and widely supported in browsers, except IE
• async/await landed in V8 and has been enabled by default since Chrome 55 (released in Dec 2016)
  • it landed in Node 7 in October 2016
  • and also landed in Firefox Nightly in November 2016

If for some weird reason you're using Node older than 7 (which has reached end of life), or are targeting old browsers, async/await can still be used via Babel (a tool that will transpile JavaScript + new features into plain old JavaScript), with the transform-async-to-generator plugin.