ES6学习笔记（ES6标准入门）-----语法一

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() {}

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

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