apply的用法

call、apply和bind的⽤法及区别

⼀、call和apply

1、call和apply都是ype的⽅法，每⼀个⽅法的对象实例newfunction（）都会有这两个属性；

2、这两个属性都是针对⽅法的属性针对⽅法使⽤；

3、call和apply使⽤⽅法相同；

4、call和apply的参数不同；

（1）(this,param1,param2,param3);//可以传多个参数

（2）(this,paramArray);//只能传两个参数，第⼆个⼀般为数组

⼆、bind

call和apply会改变this指向，然后执⾏函数；

bind会改变this指向后，返回⼀个绑定新this的函数；

三、demo

varname="aven";

varage=18;

varobj={

name:"ake",

age:,

test:function(){

("name:",,"age:",);

}

};

();

//name:akeage:undefined

//因为()只会调⽤本⾝属性，本⾝没有age属性，但是有name属性

()

//name:avenage:18

//call参数为null或undefined时默认指向window，

//this含有属性name:"aven",age:18，所以输出结果变化

varname="testName";

varage=18;

varobj={

name:"ake",

age:,

test:function(gender,home){

("name:",,"age:",,"gender:",gender,"home:",home);

}

};

varperson={

name:"aven",

age:18

}

(person,"female","China")//name:avenage:18gender:femalehome:China

(person,["female","China"])//name:avenage:18gender:femalehome:China

(person,"female","China")()//name:avenage:18gender:femalehome:China

(person,["female","China"])()//name:avenage:18gender:["female","China"]home:undefined

(this,"female","China")()//name:testNameage:18gender:femalehome:China

四、实现call⽅法

=function(){

var_this=arguments[0]

varparams=[...arguments].slice(1)

varisStrict=(function(){returnthis===undefined})

if(!isStrict){

//如果是其他原始值，需要通过构造函数包装成对象

vartype=typeof_this;

if(type==='number'){

_this=newNumber(_this)

}elif(type==='string'){

_this=newString(_this)

}elif(type==='boolean'){

_this=newBoolean(_this)

}

}

varinvokeFun=this;

if(_this===null||_this===undefined){

returninvokeFunc(...params)

}

varuniquePropName=Symbol(_this)

_this[uniquePropName]=invokeFun

return_this[uniquePropName](...params)

}

五、实现⼀个apply，跟call相似，把参数列表改为参数数组

y=function(_this,params){

varisStrict=(function(){returnthis===undefined}())

if(!isStrict){

//如果是其他原始值，需要通过构造函数包装成对象

vartype=typeof_this;

if(type==='number'){

_this=newNumber(_this)

}elif(type==='string'){

_this=newString(_this)

}elif(type==='boolean'){

_this=newBoolean(_this)

}

}

varinvokeFun=this

varinvokeParams=y(params)?params:[]

if(_this===null||_this===undefined){

returninvokeFun(...invokeParams)

}

uniquePropName=Symbol(_this)

_this[uniquePropName]=invokeFun

return_this[uniquePropName](...invokeParams)

}

六、实现bind，区别在于

=function(){

varboundTargetFunc=this;

if(typeofboundTargetFunc!=='function'){

thrownewError('绑定的⽬标必须是函数')

}

varboundThis=arguments[0];

varboundParams=[].(arguments,1);

functionfBound(){

varrestParams=[].(arguments);

varallParams=(restParams)

(thisinstanceoffBound?this:boundThis,allParams)

}

ype=(ype||ype)

returnfBound

}