js中call.apply一起用的代码，看不懂

Question

constobj={say:function(name){console.log("sayhello"+name);}};constaddSay=()=>{console.log("addSay");};varoldMethod=obj["say"];obj["say"]=function(arg){addSay.call(this,arg);returnoldMethod.call.apply(oldMethod,[this].concat(Array.prototype.slice.call(arguments)));};obj.say("allen");代码如上，其中这块代码看不懂，有懂的么obj["say"]=function(arg){addSay.call(this,arg);returnoldMethod.call.apply(oldMethod,[this].concat(Array.prototype.slice.call(arguments)));};