Run results for: Combining Object Slices

Run details:

User agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_13_6) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/93.0.4577.82 Safari/537.36

Browser: Chrome 93

Operating system: Mac OS X 10.13.6

Device Platform: Desktop

Date tested: 3 years ago

Test name	Executions per second
Reduce / Spread	354.8 Ops/sec
Map Object.entries / Object.fromEntries	4652.4 Ops/sec
Object.assign - single spread, no mutation	15430.5 Ops/sec
Object.assign - single spread, mutate first	24649.2 Ops/sec

Script Preparation code:

function createSlices(numSlices, propsPerSlice = 5) {
  const arr = [];
  const entries = [];

  for (let i = 0; i < numSlices; i++) {
    const o = {};
    for (let j = 0; j < propsPerSlice; j++) {
      const key = `key_${i}_${j}`;
      const value = `${i}_${j}`;
      o[key] = value;
      entries.push([key, value]);
    }
    arr.push(o);
  }

  return [arr, entries];
}

var [slices, entries] = createSlices(100);

Tests:

Reduce / Spread
slices.reduce((store, slice) => ({ ...store, ...slice }), {});
Map Object.entries / Object.fromEntries
Object.fromEntries( slices .map((slice) => Object.entries(slice)) .flat() );
Object.assign - single spread, no mutation
Object.assign({}, ...slices);
Object.assign - single spread, mutate first
Object.assign(...slices);
Simple fromEntries
Object.fromEntries(entries);

Run results for: Combining Object Slices

See https://www.richsnapp.com/article/2019/06-09-reduce-spread-anti-pattern

Reduce / Spread

Map Object.entries / Object.fromEntries

Object.assign - single spread, no mutation

Object.assign - single spread, mutate first

Simple fromEntries