I write a lot of tests for new features within Firefox DevTools. We have hundreds of “mochitests” which open the browser and perform synthetic actions like clicking, typing, and other user actions. I’ve previously written about waitForever which essentially halts following actions without locking the browser. Another utility I enjoy is waitForTime, an async JavaScript function that I can await to give breathing time between two tasks.

Whenever I want to wait a given amount of time between tasks, I employ this function:

function waitForTime(ms) {
  return new Promise(r => setTimeout(r, ms));

/* Usage */
await waitForTime(200);
// other thing...
await waitForTime(200);
// next thing ...

It’s important to point out that most waitForTime calls don’t appear in the final test, since arbitrary timeouts lead to intermittent test failures, but they are helpful in knowing where I need to add polling for some other condition!

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