JS: Object Overview

Object syntax basics

• JS: Object (basics)

What is object

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

• JS: Property Overview

Data object and special-purpose object

JavaScript objects can be categorized into 2 kinds:

Data object

collection of key-and-value pairs. e.g. {a:1, b:2}

also known as Object Object.

Special-purpose object

• Special purpose and may have internal data.
• For example, function, date, regex, etc, are specialized objects.
• They have special properties and behaviors.
• But they still have the feature of holding key-and-value pairs.

• JS: Object Type

Prototype of an object (parent of an object)

• Each object MAY have ONE parent object. Just one, or none. This object is call its prototype.
• The chain of parents is called Prototype Chain.
• When a property is accessed, JavaScript will go up the parent object or parent of parent etc to look for the property, until found, or no more parent. (this is called inheritance.)

• JS: Prototype and Inheritance

Is extensible

Each object may be made non-extensible, meaning, you cannot add properties to it.

• JS: Object extensible, seal, freeze

Source of 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.

• JS 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

• JS: Create Object