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);

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