Converting an Array of Objects to an Object

Lakshmi Ramasamy 23rd June 2020 Leave a Comment

In this post we will see the different ways to converting an Array to an Object. Below list are some of the ways that I have encountered during my programming career.

for loop
ES6 reduce() method
Object.fromEntries
Object.assign
Underscore and Lodash

See this post also Convert an Object to an Array in JavaScript

let we know about Object, it is something that has key and value pairs(separated by colon).

var person = {
  firstName: "John",
  lastName: "Doe",
  age: 50,
  eyeColor: "blue"
};

for loop

Simply we can iterate over the array and assign the key value pairs to the Object.

var arr = [{ key: "Name", value: "Pritha" }, { key: "Age", value: "25" }];

var result = {};
  for (var i=0, len=arr.length; i < len; i++) {
  result[arr[i].key] = arr[i].value;
}

console.log(result) // {Name: "Pritha", Age: "25"}

ES6 reduce() method

This is one of the popular way to convert array into an object. If the array is empty then it will return the empty object.

var arr = [{ key: "Name", value: "Potter" }, { key: "Age", value: "25" }];

function arrayToObject(pairs) {
		 return pairs.reduce((obj, item) => (obj[item.key] = item.value, obj) ,{});
};

console.log(arrayToObject(arr)); // {Name: "Potter", Age: "25"}

Last {} is the initial obj value for reduce function, if you won’t provide the initial value the first arr element will be used (which is probably undesirable).

`Object.fromEntries`

It is quite new method which convert the Object to an Array introduced in 2019. Make sure you only pass a key-value pair.

var arr = [{ key: "Name", value: "Helen" }, { key: "Age", value: "25" }];

console.log(Object.fromEntries(arr.map(item => [item.key, item.value]))); //{Name: "Helen", Age: "25"}

`Object.assign`

var arr = [{ key: "Name", value: "Gim" }, { key: "Age", value: "25" }];

console.log(Object.assign({}, ...arr.map(item => ({ [item.key]: item.value })))); 
//{Name: "Gim", Age: "25"}

Underscore and Lodash

const array = [
  ['Name', 'Sugumar'],
  ['Age', '25'],
];

//Lodash
_.fromPairs(array); 
//Underscore 
_.object(array);

//Output: {Name: "Sugumar", Age: "25"}