Array.of 与“[]".何时在“[]"上使用 Array.of? [英] Array.of vs "[ ]". When to use Array.of over "[ ]"?

问题描述

当我发现 Array.of.

根据 MDN，

Array.of() 方法使用可变数量的参数创建一个新的 Array 实例，而不管参数的数量或类型如何.

The Array.of() method creates a new Array instance with a variable number of arguments, regardless of number or type of the arguments.

var a = Array.of(1,2,3,4,5);
console.log(a)

但是如果我已经知道这些值，我也可以将它们包装在 [] 中以获得相同的输出.那么当我们可以/应该使用 Array.of 时，是否有特定的场景?与 [] 相比，使用它有什么好处吗?

But if I already know the values, I can also wrap them in [] to get same output. So is there a specific scenario when we can/should use Array.of? Also is there any benefit of using it over []?

这个问题的目标是Array.of vs [] 和new Array vs Array 之间的区别.

Objective of this question is difference between Array.of vs [] and not new Array vs Array.of

推荐答案

Array.of() 和 Array()/ 之间有一个细微的区别[] 构造函数.通常就像 Array() 一样，Array.of() 中的 this 将是 Array 对象，它将使用 Array.constructor 即 function Array() 来构造它的结果.

There is one subtle difference between Array.of() and Array() / [] constructor. Normally just like Array(), the this in Array.of() will be the Array object and it will use the Array.constructor which is function Array() to construct it's result.

然而 Array.of 可以通过改变它的绑定上下文来表现不同.如果绑定上下文可以用作构造函数(如果绑定对象是函数)，它将使用该函数来构造.因此，让我们将 Array.of() 绑定到一个函数，看看会发生什么.

However Array.of can behave differently by changing it's bound context. If the bound context can be used as a constructor (if the bound object is a function) it will use that function to construct. So let's bind the Array.of() to a function and see what happens.

function Test(n){console.log(n)}
Test.prototype.last = function(){return this[this.length-1]};

var what = Array.of.call(Test, [5,6,7], {a:0,b:1}, 42, null, "this is last");
console.log(JSON.stringify(what,null,2));
console.log(what.last());

所以我们得到了一个类似thingy的数组，可以访问我们构造函数原型中的所有函数方法加上那些方法.

So we got an array like thingy with access to all function methods plus the ones at our constructor's prototype.

最好记住它是定义;

NOTE 2 of 函数是有意的泛型工厂方法；它不要求它的 this 值是 Array 构造函数.因此它可以被其他构造函数转移或继承可以使用单个数字参数调用.

NOTE 2 The of function is an intentionally generic factory method; it does not require that its this value be the Array constructor. Therefore it can be transferred to or inherited by other constructors that may be called with a single numeric argument.

好的，这对于数组子类化非常方便.我知道通过涉及 Object.setPrototypeOf() 或 __proto__ 可以实现数组子类化，但它们有点不鼓励的操作，我们仍然可以在 Array.of() 的帮助下做类似的工作.所以 .. 曾经被认为是无用的 Array.of() 在这里变成了英雄；可能是最有用的 Array 方法之一.怎么来的..?让我们看看...

OK this can be very handy for array sub-classing. I know array sub-classing is possible by involving Object.setPrototypeOf() or __proto__ but they are somewhat discouraged operations and we can still do a similar job with the help of Array.of(). So .. once known to be useless Array.of() here becomes a hero; may be one of the most useful Array methods. How come..? let's see...

function SubArr(){}
SubArr.prototype = Object.create(Array.prototype); // make SubArr.prototype's prototype Array.prototype
SubArr.prototype.last = function(){return this[this.length-1]}; // add prototype methods to SubArr

var what = Array.of.call(SubArr, 1, 2, 3, 4, "this is last");
console.log(JSON.stringify(what,null,2));
console.log(what.last());
console.log(what.map(e => e));
console.log(what instanceof Array);
console.log(Array.isArray(what));
console.log(Object.prototype.toString.call(what));

我也尝试过使 SubArr.prototype.constructor = Array; 但 Array.isArray(what) 仍然导致 false.

I have also tried making SubArr.prototype.constructor = Array; but Array.isArray(what) still resulted false though.

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