How to convert an Object {} to an Array [] of key-value pairs in JavaScript?

The task is to convert an Object {} to an Array [] of key-value pairs using JavaScript. 

Objects in JavaScript are the most important data type and form the building blocks for modern JavaScript. These objects are quite different from JavaScript’s primitive data types (Number, String, Boolean, null, undefined, and symbol). Objects are more complex and each object may contain any combination of these primitive data types as well as reference data types, while the array is a single variable that is used to store different elements. It is often used when we want to store a list of elements and access them by a single variable.

Methods to convert the Objects to JavaScript Array:

Method 1: Using Object.keys() and JavaScript map()

• In this method, we will use Object.keys() and map() to achieve this. 
• By using Object.keys(), we are extracting keys from the Object then this key is passed to the map() function which maps the key and corresponding value as an array.

Syntax:

Object.keys(obj);

Parameters:

• obj: It is the object whose enumerable properties are to be returned.

Syntax:

map(function callback(currentValue[, index[, array]]){
    // Return element for new_array
}

Parameter:

• callback: Function that produces an element of the new Array

Example: In this example, a JavaScript object will be converted to an array using the Object.keys() and map() methods.

javascript

// An Object
let obj = { "1": 5, "2": 7, "3": 0, "4": 0, "5": 0 };

// Using Object.keys() and map() function
// to convert an Object {} to an
// Array [] of key-value pairs

let result = Object.keys(obj).map(function (key) {

    // Using Number() to convert key to number type
    // Using obj[key] to retrieve key value
    return [Number(key), obj[key]];
});

// Printing values
for (let i = 0; i < result.length; i++) {
    for (let z = 0; z < result[i].length; z++) {
        console.log(result[i][z]);
    }
}

Output

1
5
2
7
3
0
4
0
5
0

Method 2: Using JavaScript Object.entries() method

We will use Object.entries() which is available in JavaScript. Object.entries() method is used to return an array consisting of enumerable property [key, value] pairs of the object which are passed as the parameter. The ordering of the properties is the same as that given by looping over the property values of the object manually. 

Syntax:

Object.entries(obj);

Parameters:

• obj: It is the object whose enumerable own property [key, value] pairs are to be returned. 

Example: In this example, a javascript object will be converted to a javascript array using the Object.entries() method.

javascript

// An Object
let obj = {
    "1": 500,
    "2": 15,
    "5": 4,
    "4": 480,
    "10": 87
};

// Using Object.entries() function
// to convert an Object {} to an
// Array [] of key-value pairs
let result = Object.entries(obj);

// Printing values
for (let i = 0; i < result.length; i++) {
    for (let z = 0; z < result[i].length; z++) {
        console.log(result[i][z]);
    }
}

Output

1
500
2
15
4
480
5
4
10
87