Ready from jQuery

ready.js

function ready(fn){
	let done = false;
	
	function act(){
		if(done)return;
		done = true;
		fn();
	}

	if (
		document.readyState === "complete" ||
		(document.readyState !== "loading" && !document.documentElement.doScroll)
	){
		window.setTimeout(act, 0);
	} else {
		document.addEventListener("DOMContentLoaded", act);
		window.addEventListener("load", act);
	}
}