JavaScript - add key / value pair to object

In this article, we would like to show you how to add key / value pair to an object in JavaScript.

There are two ways to do that:

1. Using dot notation,
2. Using square bracket notation

In the below example we create obj object with two key / value pairs.
We add key3 with 'value3' using dot notation, then we display whole obj object.

Runnable example:

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var obj = {

    key1: 'value1',

    key2: 'value2'

};

​

obj.key3 = 'value3';  // <-----  add a key / value pair using dot notation

​

console.log(JSON.stringify(obj, undefined, 4));

Output:

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{

    "key1": "value1",

    "key2": "value2",

    "key3": "value3"

}

In the below example we create obj object with two key / value pairs.
We add key3 with 'value3' using square bracket notation, then we display whole obj object.

Note:
This approach is useful because you can replace 'key3' string with some variable which let us address key value dynamically using variable.

Runnable example:

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var obj = {

    key1: 'value1',

    key2: 'value2'

};

​

obj['key3'] = 'value3';  // <-----  add a key / value pair using square bracket notation

​

console.log(JSON.stringify(obj, undefined, 4));

Output:

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{

    "key1": "value1",

    "key2": "value2",

    "key3": "value3"

}