Javascript arrays created using Object.create - not real arrays?

Question

It appears that the arrays created with Object.create are similar to arrays and quacks, such as arrays, but are still not real arrays. At least with v8 / node.js.

> a = [] [] > b = Object.create(Array.prototype) {} > a.constructor [Function: Array] > b.constructor [Function: Array] > a.__proto__ [] > b.__proto__ [] > a instanceof Array true > b instanceof Array true > Object.prototype.toString.call(a) '[object Array]' > Object.prototype.toString.call(b) '[object Object]' 

Can any Javascript guru explain why this is so, and how to make my newly created array indistinguishable from a real array?

My goal is to clone data structures, including arrays, which can have custom properties. I could, of course, manually bind the properties to the newly created array using Object.defineProperty , but is there a way to do this using Object.create ?

Answer 1

The short answer is no. This article is explained in detail.

Answer 2

No, you can’t. Object.create is all about prototypes, but both [] and Object.create(Array.prototype) inherit from the same prototype.

What you call the "desired behavior of Object.prototype.toString" is an internal [[Class]] object that cannot be set using Object.create . Creating "true arrays" (with the Array class and the behavior of a special array - indexed .length properties) is possible only using array literals or calling the Array constructor .