JavaScript Const Variable Declaration

On 4 minutes, 24 seconds read By Edward

Declare Variables Using Const In JavaScript

The const keyword has been to declare variables since ECMAScript 2015 (ES6).

JavaScript variables can be declared in 4 ways. Automatically, using var, let or const.

Const is used to declare variables in a block scope with a Temporal Dead Zone (TDZ).

Variable Declaration

Glossary:

Scope

Refers to region of the code where variable is accessible.

Global Scope

Variables declared outside function or block are accessible anywhere.

Block Scope

Variables declared within block such as if or for statement are only accessible in that local scope.

Function Scope

Variables declared within function are only accessible in that local scope.

Initialization

Variables are initialized with a default value.

Immutable

Variables values cannot be changed after initialization.

Temporal Dead Zone

Variables are not accessible until execution reaches declaration point.

Declaring Variables

Const Variable Declaration
Name Description Example
const Declares block scope with mandatory initialization const num = 1;
Name Description Example

Const Variable Declaration Snippet

// OjamboShop.com Learning JavaScript Const Variable Declaration Tutorial
// Global Scope
const num1 = 1;
console.log(num1);
// Inaccessible Outside Block
if (true) {
	console.log(num1);
	const num2 = 2;
	console.log(num2);
}
// Immutable
const num2 = num1;
console.log(num2);

JavaScript Const Variable Declaration Code
OjamboShop.com Web IDE JavaScript Const Variable Declaration Code

JavaScript Const Variable Declaration Result
OjamboShop.com Web IDE JavaScript Const Variable Declaration Result


Usage

You can use any IDE or text editor and the web browser to compile and execute JavaScript code. For this tutorial, the OjamboShop.com Learning JavaScript Course Web IDE was used to input and compile JavaScript code for the const variable declaration.

Open Source

JavaScript follows the ECMAScript standard and is licensed under the W3C Software License by web browser vendors and runtime environment vendors. This allows commercial use, modification, distribution, and allows making derivatives proprietary.

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Conclusion:

JavaScript makes it easy to declare variables. Use const to declare immutable block scoped variables with the mandatory initialization.

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