Here is how you can add a key/value to an object in JavaScript:
Option 1. Use dot notation
var user = {
fname: "Alex",
lname: "Parker"
};
user.phone = "12345";
console.log(user);
Option 2. Use bracket notation
var user = {
fname: "Alex",
lname: "Parker"
};
user["phone"] = "12345";
console.log(user);
Option 3. Use Object.assigned() method
var user = {
fname: "Alex",
lname: "Parker"
};
Object.assign(user, {phone: "12345"});
console.log(user);