Its a synchronous sleep function.

synchronous_sleep.js

/*
Usage:
-------------------------------------------------
var syn_timeout = require('synchronous_timeout');
//some code
await syn_timeout.pause(300);
//some code
-------------------------------------------------
  if defined and used in a same file:
-------------------------------------------------
//some code
await pause(300);
//some code
-------------------------------------------------
*/

var pause = function(milliseconds) {
	var dt = new Date();
	while ((new Date()) - dt <= milliseconds) { /* Do nothing */ }
}

// BETTER THAN PAUSE
var sleep = function (sleep_time_ms) {
	return new Promise(resolve => setTimeout(resolve, sleep_time_ms));
}

/*
Credits: Nathan
Site: https://stackoverflow.com/questions/4122268/using-settimeout-synchronously-in-javascript
*/

// wait ms milliseconds
function wait(ms) {
  return new Promise(r => setTimeout(r, ms));
}
// Same as above function sleep but better representation and meaning

reference :
https://developers.google.com/web/fundamentals/primers/async-functions