Add new Key - Value pair to an object in JavaScript

user.newKey = newValue;

// OR

user['newKey'] = newValue;

// OR

newUser = {...user, newKey: 'newValue'};

// OR

Object.assign(user, {newKey: 'newValue'});

In JavaScript, you can add new key-value pairs (new properties) to an object using multiple syntaxes. The dot notation is the easiest: object.newKey = newValue; The bracket notation is very similar but allows key names with a dash, a hyphen, or space: object['new-key'] = newValue;

You can also use the Object.assign() method, that copies all enumerable own properties from one or more source objects to a target object. It returns the modified target object. Object.assign(user, {newKey: 'newValue'});

And finally, you can use spread object literal: newUser = {...user, newKey: 'newValue'};