JavaScript Const

The const keyword was introduced in

Variables defined with const cannot be

Redeclared

Variables defined with const cannot be

Reassigned

Variables defined with const have

Block Scope

Cannot be Reassigned

Example

const PI = 3.141592653589793;
PI = 3.14;      // This will give an error
PI = PI + 10;   // This will also give an error

Correct const PI = 3.14159265359;
Incorrect const PI;
PI = 3.14159265359;

When to use JavaScript const?

Always declare a variable with const when you know that the value should not be changed.

Use const when you declare:

A new Array

A new Object

A new Function

A new RegExp

Constant Objects and Arrays

The keyword const is a little misleading.

Reassign a constant value

Reassign a constant array

Reassign a constant object

But you CAN:

Change the elements of constant array

Change the properties of constant object

Constant Arrays

Example

const cars = ["Saab", "Volvo", "BMW"];

cars[0] = "Toyota";

cars.push("Audi");