JavaScript立即执行函数与函数劫持的作用

let _log = console.log;//将console.log的原有功能保存到_log中
console.log = function(str){//对console.log进行劫持：添加新的功能
    _log(str+'今天周五啦！')//在console.log原有输出功能之外，加入新的信息
}

(function test(){
    console.log('明天晴天~');
}())

+function(){
    console.error('Hello World');
}()

var obj = {
    name:'song',
    fun:function(age,height){
        let age = age
        let height = height
        console.log('姓名',this.name);//this指向obj
        console.log('年龄',age);
        console.log('身高',height);
    }
}
var obj2 = {
    name:'hao'
}
obj.fun(21,187);//未劫持
console.log('------------------');
obj.fun.call(obj2,22,187);//通过调用call函数将fun函数中的this进行劫持，this执行了obj2

var obj = {
    name:'song',
    fun:function(n1,n2){
        let age = n1
        let height = n2
        console.log('姓名',this.name);
        console.log('年龄',age);
        console.log('身高',height);
    }
}
var obj2 = {
    name:'hao'
}
obj.fun(21,'187cm');
console.log('------------------');
obj.fun.apply(obj2,[22,'187cm']);

let obj2 = {
    name:'小王',
    age:'22',
    height:'187cm'
}
let obj = {
    name:"小锅巴",
    age:'25',
    height:'155cm',
    fun:function(){
        console.log('姓名',this.name);
        console.log('年龄',this.age);
        console.log('身高',this.height);
    }.bind(obj2)
}
obj.fun();