async function waitForElement

waitForElement.js

let timeout = 75;
const maxTimeout = 5000;

/**
 * Async function: call with checkElement('#myElement').then((el) { ... }) .
 * Or see first block in waitForAndPrepend as per nightpool's suggestion in MR 2037
 *
 * @param {string} selector - document query selector.
 * @param {string} returnAry - run querySelectorAll rather than querySelector?
 */
async function waitForElement(selector, returnAry = false) {
	while (document.querySelectorAll(selector).length === 0) {
		timeout = Math.max(timeout*2, maxTimeout); 
		await new Promise((resolve) => setTimeout(resolve, timeout));
	}
	
	return returnAry ? document.querySelectorAll(selector) : document.querySelector(selector);
}

window.waitForElement = waitForElement