05 - Objects

Objects are a fundamental data structure in JavaScript that allow you to store collections of key-value pairs. Unlike primitive data types (strings, numbers, booleans, etc. See data types for more), objects can hold multiple values and comparatively more complex data. Each key in an object is a string that represents a property name, and each corresponding value can be of any type, including other objects, functions, and arrays.

Use Case

Objects are so vital to JavaScript because they provide a way to group data and functionality together. For example, you can create a real-world object or entity as an object with its own properties and behaviours.

Creating an Object

The most common way to create objects is to use object literals, or much like strings, you can use the new keyword.

Object Literals

Object literals are the simplest and most readable way to create objects. The object is defined using curly braces {}, with key-value pairs separated by commas.

Creating an Object I

const person = {
  name: "John Doe",
  age: 30,
  occupation: "Software Developer",
};

This example contains an object person with properties: name, age, and occupation.

Note

Objects are typically defined using the const keyword, rather than let or var. This is to retain immutability of the variable binding, while maintaining mutability of the object’s properties.

const person = {
  name: "John Doe", // Individual properties can still be changed
  age: 30,
};
 
// This will cause an error
person = {
  name: "Bob",
  age: 25,
};

For more on the difference between the variable-defining keywords, see Var, Let, & Const

Object literals are easy and efficient to write, and are best to use when making single objects.

new and Constructor Functions

Constructor functions are used to create multiple instances of objects with similar structures using the new keyword.