How to Update a const Object in JavaScript

Update a const Object in JavaScript #

Use dot or bracket notation to update the values of an object that was declared using the const keyword, e.g. obj.name = 'New Value'. The key-value pairs of an object declared using const can be updated directly, but the variable cannot be reassigned.

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const obj = {
  name: 'Tom',
  age: 30,
};

// ✅ works
obj.name = 'John';
obj.age = 29;
console.log(obj); // 👉️ {name: 'John', age: 29}

// ⛔️ doesn't work
// ❌️ Error: Assignment to constant variable.
obj = {name: 'John', age: 29};

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

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// ✅ works
const obj = {country: 'Chile'};
obj['country'] = 'Columbia';
console.log(obj); // 👉️ {country: 'Columbia'}

const example = 'hello';
// ⛔️ Error: Assignment to constant variable.
example = 'test';

If you're looking to create an object whose values cannot be updated, you have to use the Object.freeze method.

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const obj = {country: 'Chile'};

Object.freeze(obj);

obj.country = 'Columbia';
console.log(obj); // 👉️ {country: 'Chile'}

Because we used the const keyword to declare the object, the variable cannot be reassigned.

The Object.freeze method freezes the object:

• preventing the key-value pairs to be changed
• new properties to be added
• existing properties to be deleted

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.