How to create an object from two arrays in JavaScript?

Given two arrays the task is to create an object from them where the first array contains the keys of the object and the second array contains the values of the object. Return null if the array lengths are not the same or if the arrays are empty.

We can create an object from two arrays in Javascript in the following ways:

• Using for-each loop
• Using Object.assign method
• Using  reduce() method
• Using loop
• Using object.fromEntries() Method

Example:

Input:
Array 1 =>  [1, 2, 3, 4]
Array 2 =>  ["ram", "shyam", "sita", "gita"]

Output:
{
  1: "ram",
  2: "shyam",
  3: "sita",
  4: "gita"
}

Method 1: Using for-each loop

The arr.forEach() method calls the provided function once for each element of the array. The provided function may perform any kind of operation on the elements of the given array. 

Example: In this example, we will be using Javascript`s for-each loop.

Javascript

let a = [1, 2, 3, 4];
let b = ["ram", "shyam", "sita", "gita"]

// Checking if the array lengths are same
// and none of the array is empty
function convertToObj(a, b) {
    if (a.length != b.length ||
        a.length == 0 ||
        b.length == 0) {
        return null;
    }
    let obj = {};

    // Using the foreach method
    a.forEach((k, i) =>
              { obj[k] = b[i] })
    return obj;
}
console.log(convertToObj(a, b))

Output

{ '1': 'ram', '2': 'shyam', '3': 'sita', '4': 'gita' }

Method 2: Using Object.assign method

The Object.assign() method is used to copy the values and properties from one or more source objects to a target object.

Example: In this example, we will be using Javascript`s Object.assign method.

Javascript

let a = [1, 2, 3, 4];
let b = ["ram", "shyam", "sita", "gita"]

// Checking if the array lengths are same
// and none of the array is empty
function convertToObj(a, b) {
    if (a.length != b.length ||
        a.length == 0 ||
        b.length == 0) {
        return null;
    }

    // Using Object.assign method
    return Object.assign(...a.map((k, i) =>({
                          [k]: b[i] })))
}
console.log(convertToObj(a, b))

Output

{ '1': 'ram', '2': 'shyam', '3': 'sita', '4': 'gita' }

Method 3: Using reduce() method

The Javascript arr.reduce() method in JavaScript is used to reduce the array to a single value and executes a provided function for each value of the array (from left to right) and the return value of the function is stored in an accumulator. 

Example: In this example, we will be using Javascript`s reduce() method.

Javascript

let a = [1, 2, 3, 4];
let b = ["ram", "shyam", "sita", "gita"];

// Checking if the array lengths are same
// and none of the array is empty
function convertToObj(a, b) {
    if (a.length != b.length ||
        a.length == 0 ||
        b.length == 0) {
        return null;
    }

    // Using reduce() method
    let object = a.reduce((acc, element, index) => {
        return {
            ...acc,
            [element]: b[index],
        };
    }, {});

    return object;
}
console.log(convertToObj(a, b));

Output

{ '1': 'ram', '2': 'shyam', '3': 'sita', '4': 'gita' }

Method 4: Using Loop

This is the basic loop method for creating the object from the two arrays. We can iterate over one of the arrays and use the loop index to access corresponding elements from both arrays.

Example:

Javascript

function createObject(keys, values) {
    let result = {};
    let length = Math.min(keys.length, values.length);
    for (let i = 0; i < length; i++) {
        result[keys[i]] = values[i];
    }
    return result;
}

// Example usage:
let a = [1, 2, 3, 4];
let b = ["ram", "shyam", "sita", "gita"];
let result = createObject(a, b);
console.log(result);

Output

{ '1': 'ram', '2': 'shyam', '3': 'sita', '4': 'gita' }

Method 5: Using object.fromEntries() Method

The Object.fromEntries() method in JavaScript is a standard built-in object which is used to transform a list of key-value pairs into an object.

Example:

Javascript

function createObject(keys, values) {
    const obj = Object.fromEntries(
        keys.map((key, index) => [key, values[index]]),
    );

    return obj;
}

let a = [1, 2, 3, 4];
let b = ["ram", "shyam", "sita", "gita"];
let result = createObject(a, b);
console.log(result);

Output

{ '1': 'ram', '2': 'shyam', '3': 'sita', '4': 'gita' }