Performance API causes infinite loop when used with Sinon fake timers

[Sergio Cinos]

Hello,

First, I know this is technically not a bug in JSDOM or in Sinon. But the combination of those two libraries produces an infinite loop when following a pattern that is probably very common.

This is the reproduction code:

const sinon = require('sinon');

sinon.useFakeTimers();

require('jsdom'); //This line creates an infinite loop

This is caused by the new Performance API implementation (tested with JSDOM 11.6.2). The "problematic" code is:

// This function assumes the clock is accurate.

function calculateClockOffset() {

const start = Date.now();

let cur = start;

while (cur === start) {

cur = Date.now();

}

Because Sinon's fake timers mock `Date` by default, `Date.now()` will always return the same number, creating a loop.

The workaround is to use:

sandbox.useFakeTimers('setTimeout', 'clearTimeout', 'setInterval', 'clearInterval');

I suspect that using Sinon's fake timers and JSDOM is a common pattern, and developers will run into this problem in the future. I'm creating this post to start the discussion about a potential improvement (maybe stop the loop and thrown an error after 10k iterations?) and to have a link we can send to other developers complaining about this problem.

Regards,

Sergio