prefer-object-from-entries

Prefer Object.fromEntries() over Array#reduce() unicorn/prefer-object-from-entries

const demo= [{a: 1 b:3, c: 3},{a: 11 b:13, c: 13}]

const reduced = demo.reduce((acc, item) => {
  acc[item.a] = item.b

  return acc
}, {})

[fregante]

Better yet, no functions at all:

const demo= [{a: 1 b:3, c: 3},{a: 11 b:13, c: 13}]

const reduced = {};
for (const item of demo) {
	reduced[item.a] = item.b
}

.reduce() is mostly used as a generic loop. There’s nothing special in this case that justifies its awkward API.

Perf test

const array = Array.from({length: 1e2}, () => ['k', 'v'])

console.time('reduce');
for (let i = 0; i < 1e3; i++)
array.reduce((acc, item) => {
  acc[item[0]] = item[1]

  return acc
}, {})
console.timeEnd('reduce');

console.time('fromEntries');
for (let i = 0; i < 1e3; i++)
Object.fromEntries(
  array.map(item => [
    item[0], // key
    item[1], // value
  ]),
);
console.timeEnd('fromEntries');


console.time('for-of');
for (let i = 0; i < 1e3; i++) {
    const reduced = {};
    for (const item of array) {
        reduced[item[0]] = item[1]
    }
}
console.timeEnd('for-of');
VM237:10 reduce: 3.24609375 ms
VM237:20 fromEntries: 13.962158203125 ms
VM237:30 for-of: 5.65380859375 ms

[fisker]

I understand that there might be sight performance loss, but the second one is more readable to me.

I think this is acceptable.

const array = Array.from({length: 1e2}, () => ['k', 'v'])

console.time('reduce');
for (let i = 0; i < 1e3; i++)
array.reduce((acc, item) => {
  acc[item[0]] = item[1]

  return acc
}, {})
console.timeEnd('reduce');

console.time('fromEntries');
for (let i = 0; i < 1e3; i++)
Object.fromEntries(
  array.map(item => [
    item[0], // key
    item[1], // value
  ]),
);
console.timeEnd('fromEntries');
VM141:10 reduce: 4.244873046875 ms
VM141:20 fromEntries: 6.815185546875 ms

I don’t think there are not too many cases in real world that the array is already key-value pairs, most of them need to transform. Any real word cases can help us to understand why you don’t like it?

The one in the topic seems silly to me, if there are duplicated value of a property, it may result unexpected.