this

• this 要在执行时才能确认值，定义时无法确认值

var a = {
  name:'A',
  fn:function(){
    console.log(this.name);
  }
}
a.fn() //this === A
a.fn.call({name:'B'}) //this === {name:'B'}
var fn1 = a.fn;
fn1() //this === window

• 作为构造函数执行
• 作为对象属性执行
• 作为普通函数执行
• call apply bind

function Foo(name){
  this.name = name;
}
var f = new Foo('zhangsan');
var obj = {
  name:'A',
  printName:function(){
    console.log(this.name);
  }
}
obj.printName()
function fn(){
  console.log(this);
}
fn()
// call apply bind
function fn1(name) {
  alert(name);
  console.log(this);
}
fn1.call({x:100},'zhangsan',20);
// bind
var fn2 = function fn2(name) {
  alert(name);
  console.log(this);
}.bind({y:200});
fn2('zhangsan',20);

this几种不停的使用场景

• 作为构造函数执行
• 作为对象属性执行
• 作为普通函数执行
• call apply bind

function Foo(name){
  this.name = name;
}
var f = new Foo('zhangsan');
var obj = {
  name:'A',
  printName:function(){
    console.log(this.name);
  }
}
obj.printName()
function fn(){
  console.log(this);
}
fn()
// call apply bind
function fn1(name) {
  alert(name);
  console.log(this);
}
fn1.call({x:100},'zhangsan',20);
// bind
var fn2 = function fn2(name) {
  alert(name);
  console.log(this);
}.bind({y:200});
fn2('zhangsan',20);