JS: Array-Like Object

What is a array-like object

A object such that is all of the following:

• Array.isArray(obj) returns false.
• Has a property "length" with value of non-negative integer, and typically it has the Enumerable attribute false.
• Typically has property names of non-negative string integers {"0", "1", "2", etc} up to the length -1.

Create a Array-Like Object

// create array-like object
let xx = { 0: "a", 1: "b", length: 2 };
Reflect.defineProperty(xx, "length", { enumerable: false });

console.log(xx);
// { "0": "a", "1": "b" }

// create array-like object using Object.create in one shot

const xal = Object.create(
 Object.prototype,
 {
  "0": { value: "a", writable: true, enumerable: true, configurable: true },
  "1": { value: "b", writable: true, enumerable: true, configurable: true },
  "length": { value: 2, writable: true, enumerable: false, configurable: true },
 },
);

console.log(xal);
// { "0": "a", "1": "b" }

Difference Between Array vs Array-Like Object

• JS: Difference of Array vs Array-Like Object

Check if a object is true array

• JS: Array.isArray

Where does array-like object came from

• arguments (object) is a array-like object.
• In web browser, method such as document.getElementsByClassName return array-like objects. 〔see Get Element by ID, Name, Class etc〕
• new String("abc") creates a array-like object. 〔see String Constructor〕

Convert array-like object to array

• JS: Convert Array-Like Object to Array

Array-like object is a major wart in JavaScript

It is a JavaScript design warts.

whenever you see it, best is to convert it to true array right away.

Get Property Values of Array-Like Object

• JS: List Properties