How to convert an array to an object in Javascript without using loops?

Question

I want to convert the following array:

['a', 'b', 'c']

to the following object:

{a: 'a', b: 'b', c: 'c'}

How do I do it without using loop, ofcourse?

Solution 1

You'll want to use the Array.reduce() method.

The reduce() method executes a reducer function (that you provide) on each member of the array resulting in a single output value.

arr.reduce(callback[, initialValue])

The reduce() callback method takes accumulator and currentValue parameters.

• accumulator: Value is remembered throughout each iteration of the method and ultimately becomes the final returned value.
• currentValue: The current element being processed in the array.

The {} is supplied as the last argument to reduce() as the initial value to start with. And with each iteration of the Array, we add to it ultimately creating the final Object.

Example: (ES6)

const letters = ['a', 'b', 'c'];

const obj = letters.reduce((accumulator, currentValue) => {
  accumulator[currentValue] = currentValue;
  return accumulator;
}, {});

console.log(obj);

Example: (ES5)

var letters = ['a', 'b', 'c'];

var obj = letters.reduce(function (accumulator, currentValue) {
  accumulator[currentValue] = currentValue;
  return accumulator;
}, {});

console.log(obj);

Reference: Array.prototype.reduce() mozilla documentation.

Solution 2

You could map objects and join to a single object with Object.assign.

var array = ['a', 'b', 'c'],
    object = Object.assign(...array.map(v => ({ [v]: v })));
    
console.log(object);

Solution 3

An alternative solution, you can also use the newer Object.fromEntries with map as well.

let arr = ['a', 'b', 'c'];

let obj = Object.fromEntries(arr.map(m => [m,m]));

console.log(obj);

Solution 4

You may use Array#reduce to get the desired result.

const a = ['a', 'b', 'c'];
const o = a.reduce((s, a) => {
   s[a] = a;
   return s;
}, {});

console.log(o);

Solution 5

Use reduce

var arr = ['a', 'b', 'c'];


var obj = arr.reduce(function(obj, value) {
     obj[value] = value;
     return obj
}, {});
console.log(obj)

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Comments

[loveTrumpsHate]

Any way to do this without using map?

[Nina Scholz]

why not with map?

[loveTrumpsHate]

map is fine but something shorter using spread operator, maybe?

[ikwuje]

@trincot thanks for mentioning. I actually thought they were the same,