Run results for: flatmap vs reduce to filter undefined elements

Run details:

User agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:124.0) Gecko/20100101 Firefox/124.0

Browser: Firefox 124

Operating system: Mac OS X 10.15

Device Platform: Desktop

Date tested: one year ago

Test name	Executions per second
flatMap	5827.2 Ops/sec
reduce	8954.1 Ops/sec

Script Preparation code:

const myArray = [];

for (let i = 0; i < 10000; i++) {
  const obj = {
    prop1: `value${i}_1`,
    prop2: `value${i}_2`,
    prop3: `value${i}_3`,
    prop4: `value${i}_4`,
  };

  // Randomly add the metadata property
  if (Math.random() < 0.5) {
    obj.metadata = {
      info1: `metadata${i}_1`,
      info2: `metadata${i}_2`,
    };
  }

  myArray.push(obj);
}

Tests:

flatMap
myArray.flatMap(obj => { if (obj.metadata) { return { prop1: obj.prop1, metadata: obj.metadata }; } else { return []; } })
reduce
myArray.reduce((acc, obj) => { if (obj.metadata) { acc.push({ prop1: obj.prop1, metadata: obj.metadata }); } return acc; }, []);

Run results for: flatmap vs reduce to filter undefined elements

flatMap

reduce