JS to determine whether it is the first time to browse the web page

if(document.cookie.indexOf("a=hello")==-1){
			// ????alert(" Open for the first time ！");
			????var?t=new?Date(new?Date().getTime()+1000*60*60*24*30);
			????document.cookie="a=hello;?expires="+t.toGMTString();
			}else{
			// ????alert(" Open again ！");
			    this.advertisements=false
			}

Just use it directly in the load