一个关于 JavaScript 的 slice 和 splice 方法的问题 [英] A question about JavaScript's slice and splice methods

问题描述

我遇到了以下代码:

var f = function () {
    var args = Array.prototype.slice.call(arguments).splice(1);

    // some more code 
};

基本上，args 中的结果是一个数组，它是 arguments 的副本，没有第一个元素.

Basically, the result in args is an array that is a copy of the arguments without its first element.

但我无法确切理解的是为什么 f 的 arguments(这是一个将函数的输入参数保存到类似数组的对象中的对象)对象正在传递给 slice 方法以及 slice(1) 如何移除第一个元素(位于索引 0).

But what I can't understand exactly is why f's arguments (which is an object that holds the function's inputted arguments into an array-like object) object is being passed to the slice method and how slice(1) is removing the first element (positioned at index 0).

谁能帮我解释一下?

P.S.代码来自这个部分应用函数

推荐答案

<注意>
来自 链接答案是:

var args = Array.prototype.slice.call(arguments, 1);

即切片"，而不是拼接"
</注意>

i.e. "slice", not "splice"
</Note>

首先，slice 方法常用于复制它被调用的数组:

var a = ['a', 'b', 'c'];
var b = a.slice();  // b is now a copy of a
var c = a.slice(1); // c is now ['b', 'c']

所以简短的回答是代码基本上是在模拟:

So the short answer is that the code is basically emulating:

arguments.slice(1); // discard 1st argument, gimme the rest

但是你不能直接这样做.特殊arguments 对象(在所有 JavaScript 函数的执行上下文)，尽管 Array-like 支持通过带有数字键的 [] 运算符进行索引，但实际上并不是一个数组；你不能.push到它上面，.pop关闭它，或者.slice它，等等.

However you can't do that directly. The special arguments object (available inside the execution context of all JavaScript functions), although Array-like in that it supports indexing via the [] operator with numeric keys, is not actually an Array; You can't .push onto it, .pop off it, or .slice it, etc.

代码实现这一点的方式是通过欺骗"slice 函数(该函数在 arguments 对象上同样不可用)在上下文中运行 参数，通过 <代码>Function.prototype.call:

The way the code accomplishes this is by "tricking" the slice function (which again is not available on the arguments object) to run in the context of arguments, via Function.prototype.call:

Array.prototype.slice // get a reference to the slice method
                      // available on all Arrays, then...
  .call(              // call it, ...
    arguments,        // making "this" point to arguments inside slice, and...
    1                 // pass 1 to slice as the first argument
  )

Array.prototype.slice.call(arguments).splice(1) 完成同样的事情，但是对 splice(1) 进行了一个无关的调用，它从 Array.prototype.slice.call(arguments) 返回的数组中删除 个元素，从索引 1 开始并继续到数组的末尾.splice(1) 在 IE 中不起作用(从技术上讲，它缺少第二个参数，告诉它要删除 IE 和 ECMAScript 需要多少项).

Array.prototype.slice.call(arguments).splice(1) accomplishes the same thing, but makes an extraneous call to splice(1), which removes elements from the array returned from Array.prototype.slice.call(arguments) starting at index 1 and continuing to the end of the array. splice(1) doesn't work in IE (it's technically missing a 2nd parameter telling it how many items to remove that IE and ECMAScript require).

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