Why when I create an object with an array prototype I get an object

Question

I created the variable p with a prototype array

const p = Object.create([])
console.log(p)

I have got the next result in Firefox Object { }, and chrome Array {}. When I use array methods they work as they should

p.push(1)
console.dir(p) //Object { 0: 1, length: 1 } OK

But when I use the assignment operator, I get the next result

p[1] = 2
console.dir(p) // Object { 0: 1, 1: 2, length: 1 } length !!!

Hey, as documentation suggests Object.create returns an Object. It will only look like an Array though, as you've passed its prototype to it - it'll have instance methods like any Array instance. developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/… — Ivar
– Ivar, Commented Nov 9, 2020 at 9:37

York Chen · Accepted Answer · 2020-11-09 09:42:49Z

2

The Object.create() method creates a new object, using an existing object as the prototype of the newly created object.

So the result of Object.create([]) is an object. When you use "push" method for this object, actually it is found by following sequence:

So when push is execute, the length is changed to 1. But if you assign value by yourself like

p[1] = 2

it is just a property under p object, length is not changed.

answered Nov 9, 2020 at 9:32

York Chen

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Comments

laicuRoot · Accepted Answer · 2020-11-09 09:21:13Z

0

You need to use the Array constructor to create an Array. Also bear in mind that Arrays are also objects.

Taking the example from mozilla:

let fruits = new Array('Apple', 'Banana');

console.log(fruits.length); // 2
console.log(fruits[0]);     // "Apple"

Good luck in your learnings :)

answered Nov 9, 2020 at 9:21

laicuRoot

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