Add key/value pair to an object in JavaScript

This tutorial will show you how you can add key/value pair to an object in JavaScript. Here are some examples below to add key/value pair to an object.

Using dot notation

We can access an object property by using dot notation. Here is the JavaScript program below to add key/value pair to an object.

Here is the Javascript program below:

var myObj = {
    name: "sam",
    lastName: "Raja"
};

myObj.age = 32;

console.log(myObj);

In the above program, I have defined an object myObj with two properties name and lastName.

Then added a new property age to the object and set its value to 32.

After that, I logged the entire object to the console using console.log(myObj).

Output:

{ name: 'sam', lastName: 'Raja', age: 32 }

Using square bracket notation

The square bracket notation is also a way that is used to access an object property. The object properties can be accessed using a string as the property. We can also use the square bracket notation to set the value of an object property.

Here is a JavaScript program to add key/value pair to an object using square bracket notation.

var myObj = {
    name: "sam",
    lastName: "Raja"
};

myObj["age"] = 32;

console.log(myObj);

Output:

{ name: 'sam', lastName: 'Raja', age: 32 }

Using the object.assign method

An object can be copied by the object.assign method into a single object that contains all enumerable own properties of a given object.

Here is the JavaScript program below:

var myObj = {
    name: "sam",
    lastName: "Raja"
};

Object.assign(myObj, {age: 32});

console.log(myObj);

In the above program, Object.assign() will copy the age property from the object {age: 32} to the myObj object.

Now, the myObj object has an age property with a value 32.

Output:

{ name: 'sam', lastName: 'Raja', age: 32 }

Using the spread operator (…)

We can use the spread operator (...) to add key/value pair to an object. We can create a new object by this operator that contains all the properties of the original object and add a new property with the specified value.

Here is the JavaScript program below:

var myObj = {
    name: "sam",
    lastName: "Raja"
};

const newObj = { ...myObj, age : 32 };

console.log(newObj);

Output:

{ name: 'sam', lastName: 'Raja', age: 32 }