JavaScript Const

const is a keyword in JavaScript used for declaring variables that cannot be reassigned. It was introduced in ECMAScript 6 (ES6) and is used in place of the var and let keywords in modern JavaScript code. In this article, we will cover how to use const and its advantages over other variable declarations.

Declaring Constants with const

To declare a constant with const, use the following syntax:

const constantName = value;

Here’s an example of declaring a constant x with const:

const x = 5;

Once a value has been assigned to a constant, it cannot be reassigned. For example, the following code will throw an error:

const x = 5;
x = 10; // Throws an error: "Uncaught TypeError: Assignment to constant variable." 

Scoping with const

Like let, const variables also have block scope. This means that const variables are only accessible within the block of code they are declared in.

Here’s an example of using const to create a variable y that is only accessible within the if statement block:

if (true) {
  const y = 5;
}
console.log(y); // Throws an error: "Uncaught ReferenceError: y is not defined"

Advantages of const

The main advantages of using const are:

1. Immutable: const variables are immutable, which means that once a value has been assigned to them, it cannot be reassigned. This makes code easier to reason about and less prone to bugs.
2. Block scope: const variables have block scope, which makes code easier to reason about and less prone to bugs.
3. No hoisting: const variables are not hoisted, which means they cannot be accessed before they are declared.

When to use const

You should use const in JavaScript when you want to declare variables that cannot be reassigned. This can be helpful in preventing accidental variable overwriting and improving the readability of your code.

However, keep in mind that const variables are not always appropriate. For example, if you need to declare a variable that will be reassigned later in your code, you should use let instead.

In summary, const is a keyword in JavaScript used for declaring variables that cannot be reassigned. It has several advantages over other variable declarations, including immutability and block scope. By using const in your JavaScript code, you can make your code easier to read, reason about, and maintain.