拓展原有函数的功能

function say(){
    console.log("say",arguments)
}

Function.prototype.beforeSay = function(callback){
    return (...args)=>{
        callback()
        // 调用原函数
        this(...args)
    }
}

say.beforeSay(function(){
    console.log("beforeSay")
})("hello", "world")