为什么在方法上调用（调用）和在obj上调用方法之间有区别 [英] why there is a difference between calling (call) on a method and calling the method on the obj

问题描述

对不起，我真的应该问为什么存在差异

sorry I really should of asked why there is a differnce ,

`Object.prototype.toString.call(o).slice(x,y);`

还有这个？

o.toString().slice(x.y);

//为什么它们不同，调用应更改被调用方法$ b的 this值$ b //和toString已被继承，

// why those are different , call should change the 'this' value for the called method // and toString is already inherited ,

var x = 44 ;


`Object.prototype.toString.call(x)`; //"[object Number]"

x.toString(); // '44'

推荐答案

您没有呼叫< a href = https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Global_Objects/Function/call rel = nofollow> .call 上的方法：

You're not calling .call on the method here:

Object.prototype.toString(o).slice(x,y);

相反，您只需调用方法（在原型对象上）以 o 作为参数。

Instead, you just call the method (on the prototype object) with o as an argument.

要获取等效的方法来调用

To get an equivalent method to call to

o.toString().slice(x.y);

（在上调用方法o 对象，不带参数），则需要使用

(which calls the method on the o object, with no arguments), you will need to use

o.toString.call(o).slice(x.y);

---

---

为什么 x.toString（）与 Object.prototype.toString.call（x）吗？

因为 x = 44 是一个数字，并且当您访问 x.toString时，您将获得 Number.prototype.toString 方法而不是 Object.prototype.toString 方法。您也可以写

Because x = 44 is a number, and when you access x.toString you get the Number.prototype.toString method not the Object.prototype.toString method. You could also write

Number.prototype.toString.call(x)

获得 44 。

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