Convert Array to Object


Question

What is the best way to convert:

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

to:

{
  0: 'a',
  1: 'b',
  2: 'c'
}
1
414
9/17/2018 8:58:17 AM

Accepted Answer

ECMAScript 6 introduces the easily polyfillable Object.assign:

The Object.assign() method is used to copy the values of all enumerable own properties from one or more source objects to a target object. It will return the target object.

Object.assign({}, ['a','b','c']); // {0:"a", 1:"b", 2:"c"}

The own length property of the array is not copied because it isn't enumerable.

Also, you can use ES6 spread syntax to achieve the same result:

{ ...['a', 'b', 'c'] }
336
1/18/2019 9:26:51 AM

With a function like this:

function toObject(arr) {
  var rv = {};
  for (var i = 0; i < arr.length; ++i)
    rv[i] = arr[i];
  return rv;
}

Your array already is more-or-less just an object, but arrays do have some "interesting" and special behavior with respect to integer-named properties. The above will give you a plain object.

edit oh also you might want to account for "holes" in the array:

function toObject(arr) {
  var rv = {};
  for (var i = 0; i < arr.length; ++i)
    if (arr[i] !== undefined) rv[i] = arr[i];
  return rv;
}

In modern JavaScript runtimes, you can use the .reduce() method:

var obj = arr.reduce(function(acc, cur, i) {
  acc[i] = cur;
  return acc;
}, {});

That one also avoids "holes" in the array, because that's how .reduce() works.


Licensed under: CC-BY-SA with attribution
Not affiliated with: Stack Overflow
Icon