jQuery中$(function())的作用

$(function(){//五分钟无操作，返回系统首页,timeToreturn.js
    function timeToReturn(){
        window.location.href = "http://localhost:8080/zhongCourt/";
    }
    var nowtime = Date.parse(new Date());
    var timeend = Date.parse(new Date());
 
    $("body").click(function(){
        nowtime = Date.parse(new Date());
        console.log("nowtime" + nowtime);   
    });
 
    function check(){
        timeend = Date.parse(new Date());
        console.log("check");
        if((timeend - nowtime) > 300000){
            timeToReturn();
        }
        setTimeout(check,10000);
    }
    setTimeout(check,10000);
    
})