Javascript数组原型

Question

由于Array.prototype本身是此处的array（[]） 引用 ，如果我们必须替换本机原型，我们如何放置文字对象，而我们需要放置文字数组，不是吗？

Array.prototype=[]

Answer 1

There's no point in assigning a new array to Array.prototype . It's usually a read-only property and the assignment will fail silently.

> a = []
[]
> a === Array.prototype
false
> Array.prototype = a
[]
> a === Array.prototype
false

Even if the assignment were to succeed, the replacement array would of necessity have been created with the original prototype in place. Thus, the original prototype would be the [[prototype]] of the new prototype object and all the native methods would still be found in the prototype chain of any array created after the assignment.

If you want to replace (hide) a native instance method of Array (eg, push ), just assign the new method to the appropriate property:

Array.prototype.push = . . .;

Also, see this answer for how you might extend a native method (such as push ). (Unless you're just extending a native method in some way, I can't imagine a use case where this is anything other than a really bad thing to do. Even then...)

Answer 2

EcmaScript 5, the latest version of JavaScript, changed the meaning of

[]

from

 new Array()

to create using the original Array constructor instead of looking up the name Array in scope as earlier versions of JavaScript did.

The EcmaScript 5 specification says

11.1.4 Array Initialiser

...

The production ArrayLiteral : [ Elision _opt ] is evaluated as follows:

1. Let array be the result of creating a new object as if by the expression new Array() where Array is the standard built-in constructor with that name.

The bolded text is new in EcmaScript 5, and means that the meaning of [] is not affected by any subsequent modifications to the Array global or its members including its prototype.