ES6学习笔记（ES6标准入门）-----语法一

1. js中的变量提升和函数提升

    console.log(tmp);  #undefined
    var tmp = 123;
    console.log(tmp);  #123
    
    #其实上边代码按照下边执行
    var tmp;
    console.log(tmp);
    tmp = 123;
    console.log(tmp);
   
    #函数提升
    console.log(f1);  #function() {}
    console.log(f2);  #undefined
    function f1() {}
    var f2 = function() {}
   

2. 使用var声明的变量和不使用的情况

    function c() {
      a = 123;  //相当于window.a = 123;
    }
    c();
    alert(a);  //123
    
    function d() {
      var b = 456;
    }
    d();
    alert(b);  //报错
   

3. 关于ES5的call和apply

    var cat = function() {
        this.voice = "miaomiao";
        this.food = "yu";
        this.eat = function(){
            console.log('eating ' + this.food);
        }
    }
   
    var dog = function() {
        this.voice = "wangwang";
        this.food = "gutou";
        this.miao = function(voice1, voice2){
            console.log(this.voice);
            if(typeof voice1 !== "undefined") {
                console.log(voice1);
            }
            if(typeof voice2 !== "undefined") {
                console.log(voice2);
            }
        }
    }
    
    c = new cat();
    d = new dog();
    c.eat();
    d.miao();
    c.eat.call(d);
    d.miao.call(c, "wang1", "wang2");
    d.miao.apply(c, ["wang1", "wang2"]);
   
    t = c.eat.bind(d);
    t();  //gutou