apply和call的效果和異同

相同點

1.將第一個傳入對象變爲函數this的指向

let s = function(){console.log(this)}
let k = {a:123,b:312}

s() //Window 對象
s.apply(k)  // {a:123,b:312} 
s.call(k)   // {a:123,b:312} 

2.將傳入的第二個參數，傳給函數
 

let c = [1]
let func = function(a){console.log(a)}
func.apply(null,c) //1
func.call(null,c)  //[1]

 

不同點

1.apply的第二個參數只接受數組,傳入對象不顯示，傳入其他報錯(call不受限制)
 

let c = {a:1}
let b = [1,2,3]
let k = '123'
let func = function(a){console.log(a)}
func.apply(null,c) //undefined
func.apply(null,b) // 1
func.apply(null,k) // error

2.apply會對傳入的第二個參數進行分解，call整個傳入

let c = [1,2,3,4]
let func = function(){console.log(arguments)}
func.apply(null,c) //[1,2,3,4]
func.call(null,c)  //[[1,2,3,4]]

//更直觀一點
let func = function(){console.log(arguments[0])}
func.apply(null,c) //1
func.call(null,c)  //[1,2,3,4]

如果對arguments不瞭解，再舉個不用arguments的栗子

let c = [1,2,3,4]
let func = function(a,b,c,d){console.log(a,b,c,d)}
func.apply(null,c) //1,2,3,4
func.call(null,c)  //[1,2,3,4] undefined undefined undefined