JavaScript Array Const

Introduction

In JavaScript, variables can be declared using three different keywords: var, let, and const. The var keyword has been used for a long time to declare variables, but let and const were introduced in ES6 (ECMAScript 2015) to address some of the issues with var. While let and const are similar in many ways, there are some key differences between them. In this article, we will focus on the use of const with arrays in JavaScript.

Declaring an Array with const

When declaring a variable with the const keyword, we are indicating that the value of the variable will not change after initialization. In the case of an array, this means that we can’t reassign the entire array to a new value. However, we can still modify the contents of the array.

Here’s an example of declaring an array with const:

const numbers = [1, 2, 3, 4, 5];

In this example, we have declared a constant variable numbers and assigned an array to it. We can access and modify the elements of the array just like any other array.

console.log(numbers[0]); // 1

numbers[0] = 6;
console.log(numbers); // [6, 2, 3, 4, 5]

As you can see, we are able to modify the elements of the array, even though the variable itself is declared with const.

Limitations of const with Arrays

While we can modify the contents of an array declared with const, there are some limitations to using const with arrays. One limitation is that we can’t reassign the entire array to a new value.

const numbers = [1, 2, 3, 4, 5];
numbers = [6, 7, 8, 9, 10]; // TypeError: Assignment to constant variable.

In this example, we are trying to reassign the entire numbers array to a new value, but we get a TypeError because numbers is declared with const.

Another limitation is that we can’t modify the length of the array.

const numbers = [1, 2, 3, 4, 5];
numbers.push(6); // TypeError: Cannot add property 5, object is not extensible

In this example, we are trying to add a new element to the end of the numbers array using the push() method, but we get a TypeError because numbers is declared with const.

In summary, when declaring an array with const in JavaScript, we are indicating that the value of the variable will not change after initialization, but we can still modify the contents of the array. However, we can’t reassign the entire array to a new value or modify its length. It’s important to keep these limitations in mind when deciding whether to use const with arrays in our JavaScript code.