JS: Object Overview

By Xah Lee. Date: . Last updated: .

Object Tutorial

If you don't know how to create object, read properties, first see

What is JavaScript Object

A JavaScript Object is a collection of key/value pairs. e.g. {a:1, b:2}. Each key/value pair is called a Property .

Special Object and Data Object

JavaScript objects can be categorized into 2 kinds:

〔see Object Type

Prototype of an Object (Parent)

this is called Prototype-Based Object System

〔see Prototype and Inheritance

IsExtensible

Each object has a special true/false value attached called the [[isExtensible]] internal slot. It specifies whether new properties can be added to the object.

〔see Prevent Adding Property

Standard Object, Hosted Object, User-Created Object

It is useful to distinguish objects by where they came from. We have the following sources:

Standard Object
Objects from the JavaScript language. e.g. arrays, functions, dates, regex, etc. 〔see JavaScript Object Reference
Hosted Object
Objects from the hosting environment. e.g. in Browser, there's Browser's Window Object. In deno, there is deno object, with properties such as version etc.
User-defined Object (Data Object)
User defined. e.g. let x = {a:1, b:2}.

Create Object

JavaScript Object Property Overview

JavaScript, Object and Inheritance