How do I convert array of Objects into one Object in JavaScript?

Question

I have an array of objects:

[ 
  { key : '11', value : '1100', $$hashKey : '00X' },
  { key : '22', value : '2200', $$hashKey : '018' }
];

How do I convert it into the following by JavaScript?

{
  "11": "1100",
  "22": "2200"
}

Answer 1

Tiny ES6 solution can look like:

var arr = [{key:"11", value:"1100"},{key:"22", value:"2200"}];
var object = arr.reduce(
  (obj, item) => Object.assign(obj, { [item.key]: item.value }), {});

console.log(object)

Also, if you use object spread, than it can look like:

var object = arr.reduce((obj, item) => ({...obj, [item.key]: item.value}) ,{});

One more solution that is 99% faster is(tested on jsperf):

var object = arr.reduce((obj, item) => (obj[item.key] = item.value, obj) ,{});

Here we benefit from comma operator, it evaluates all expression before comma and returns a last one(after last comma). So we don't copy obj each time, rather assigning new property to it.

Answer 2

Trying to fix this answer in How do I convert array of Objects into one Object in JavaScript?,

this should do it:

var array = [
    {key:'k1',value:'v1'},
    {key:'k2',value:'v2'},
    {key:'k3',value:'v3'}
];
var mapped = array .map(item => ({ [item.key]: item.value }) );
var newObj = Object.assign({}, ...mapped );
console.log(newObj );

---

One-liner:

var newObj = Object.assign({}, ...(array.map(item => ({ [item.key]: item.value }) )));

Answer 3

You're probably looking for something like this:

// original
var arr = [ 
  {key : '11', value : '1100', $$hashKey : '00X' },
  {key : '22', value : '2200', $$hashKey : '018' }
];

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

console.log(result);

Answer 4

I like the functional approach to achieve this task:

var arr = [{ key:"11", value:"1100" }, { key:"22", value:"2200" }];
var result = arr.reduce(function(obj,item){
  obj[item.key] = item.value; 
  return obj;
}, {});

Note: 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).

https://jsfiddle.net/GreQ/2xa078da/

Answer 5

Using Object.fromEntries:

const array = [
    { key: "key1", value: "value1" },
    { key: "key2", value: "value2" },
];

const obj = Object.fromEntries(array.map(item => [item.key, item.value]));

console.log(obj);

Answer 6

A clean way to do this using modern JavaScript is as follows:

const array = [
  { name: "something", value: "something" },
  { name: "somethingElse", value: "something else" },
];

const newObject = Object.assign({}, ...array.map(item => ({ [item.name]: item.value })));

// >> { something: "something", somethingElse: "something else" }

Answer 7

Use lodash!

const obj = _.keyBy(arrayOfObjects, 'keyName')

Answer 8

you can merge array of objects in to one object in one line:

const obj = Object.assign({}, ...array);

Answer 9

Based on answers suggested by many authors, I created a JsPref test scenario. https://jsperf.com/array2object82364

Below are the screenshots of performance. It is a little shocking to me to see, chrome result is in contrast to firefox and edge, even after running it several times.

Answer 10

Update: The world kept turning. Use a functional approach instead.

Here you go:

var arr = [{ key: "11", value: "1100" }, { key: "22", value: "2200" }];
var result = {};
for (var i=0, len=arr.length; i < len; i++) {
    result[arr[i].key] = arr[i].value;
}
console.log(result); // {11: "1000", 22: "2200"}

Answer 11

Using Underscore.js:

var myArray = [
  Object { key="11", value="1100", $$hashKey="00X"},
  Object { key="22", value="2200", $$hashKey="018"}
];
var myObj = _.object(_.pluck(myArray, 'key'), _.pluck(myArray, 'value'));

Answer 12

Nearby 2022, I like this approach specially when the array of objects are dynamic which also suggested based on @AdarshMadrecha's test case scenario,

const array = [ 
  { key : '11', value : '1100', $$hashKey : '00X' },
  { key : '22', value : '2200', $$hashKey : '018' }];
  
let obj = {};
array.forEach( v => { obj[v.key] = v.value }) //assign to new object
console.log(obj) //{11: '1100', 22: '2200'}

Answer 13

let array = [
  { key: "key1", value: "value1" },
  { key: "key2", value: "value2" },
];

let arr = {};

arr = array.map((event) => ({ ...arr, [event.key]: event.value }));

console.log(arr);

Answer 14

Here's how to dynamically accept the above as a string and interpolate it into an object:

var stringObject = '[Object { key="11", value="1100", $$hashKey="00X"}, Object { key="22", value="2200", $$hashKey="018"}]';

function interpolateStringObject(stringObject) {
  var jsObj = {};
  var processedObj = stringObject.split("[Object { ");
  processedObj = processedObj[1].split("},");
  $.each(processedObj, function (i, v) {
      jsObj[v.split("key=")[1].split(",")[0]] = v.split("value=")[1].split(",")[0].replace(/\"/g,'');
  });

  return jsObj
}

var t = interpolateStringObject(stringObject); //t is the object you want

http://jsfiddle.net/3QKmX/1/

Answer 15

// original
var arr = [{
    key: '11',
    value: '1100',
    $$hashKey: '00X'
  },
  {
    key: '22',
    value: '2200',
    $$hashKey: '018'
  }
];

// My solution
var obj = {};
for (let i = 0; i < arr.length; i++) {
  obj[arr[i].key] = arr[i].value;
}
console.log(obj)

Answer 16

You can use the mapKeys lodash function for that. Just one line of code!

Please refer to this complete code sample (copy paste this into repl.it or similar):

import _ from 'lodash';
// or commonjs:
// const _ = require('lodash');

let a = [{ id: 23, title: 'meat' }, { id: 45, title: 'fish' }, { id: 71, title: 'fruit' }]
let b = _.mapKeys(a, 'id');
console.log(b);
// b:
// { '23': { id: 23, title: 'meat' },
//   '45': { id: 45, title: 'fish' },
//   '71': { id: 71, title: 'fruit' } }