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Run results for:
reduce.concat() vs flatMap()
Compare the new ES6 spread operator with the traditional concat() method
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<iframe src="https://measurethat.net/Embed?id=599802" width="100%" height="500px"></iframe>
Run details:
User agent:
Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/135.0.0.0 Safari/537.36
Browser:
Chrome 135
Operating system:
Mac OS X 10.15.7
Device Platform:
Desktop
Date tested:
one year ago
Benchmark engine:
Benchmark.js
Array.prototype.flatMap
1.5M/s
reduce + Array.prototype.concat
1.0M/s
View exact numbers
Test name
Executions per second
✓
Array.prototype.flatMap
1,498,491 Ops/sec
reduce + Array.prototype.concat
1,020,209 Ops/sec
Script Preparation code:
var flag = { a: {'truthy': true, 'falsey': false, 'only-in-a': true}, b: {'truthy': true, 'falsey': false, 'only-in-b': true}, unused: {'truthy': true, 'falsey': false}, }; var rollNames = ['a', 'b', 'missing'];
Tests:
reduce + Array.prototype.concat
var other = rollNames.flatMap(rollName => // convert flag object to array containing the names of all fields with a truthy value Object.entries(flag[rollName] ?? {}).reduce((opts, [key, value]) => opts.concat(value ? key : []), []) ).reduce((unique, option) => { // ensure option entries are unique return unique.includes(option) ? unique : unique.concat(option); }, []);
Array.prototype.flatMap
var other = [...new Set(rollNames.flatMap(rollName => // convert flag object to array containing the names of all fields with a truthy value Object.entries(flag[rollName] ?? {}).flatMap(([key, value]) => value ? [key] : []) ))];