How to Update a Const Array in JavaScript

Update a Const Array in JavaScript #

Use bracket notation to update the values of an array that was declared using the const keyword, e.g. arr[0] = 'new value'. The elements of an array declared using const can be updated directly, but the variable cannot be reassigned.

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const arr = ['hello', 'world'];

// ✅ works
arr[0] = 'test';
console.log(arr); // ['test', 'world']

// ⛔️ doesn't work
// 👇️ Error: Assignment to constant variable.
arr = ['test', 'world'];

When a variable is declared using the const keyword, the variable cannot be reassigned, however if the variable is an array or an object, its values can directly be updated.

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// ✅ works
const arr = ['one']
arr[0] = 'two'
console.log(arr); // 👉️ ['two']


const test = 'one'
// ⛔️️ Error: Assignment to constant variable.
test = 'two';

If you need to create an array whose values cannot be changed, you can use the Object.freeze method.

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const arr = ['apple', 'banana'];

Object.freeze(arr);

arr[0] = 'pear';
console.log(arr); // 👉️ {country: 'Chile'}

The Object.freeze method is used to freeze an array or an object.

After an array is frozen:

• its elements cannot be changed
• new elements cannot be added to the array
• existing elements cannot be removed from the array

In closing, declaring a variable using the const keyword means that the variable cannot be reassigned, it doesn't make the value stored in the variable immutable.