mylib

添加jQuery

F12打开控制台，先检查有没有jQuery，如果没有就添加

;(function(){
	if(typeof(jQuery) != "undefined"){	
        	console.log("no need to add jQuery again");
	}else{
		var script = document.createElement("script");
		script.setAttribute("src","https://cdnjs.cloudflare.com/ajax/libs/jquery/3.2.1/jquery.min.js");
		document.body.appendChild(script);
		console.log("jQuery is added");
	}
})();