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jsPerf.app is an online JavaScript performance benchmark test runner & jsperf.com mirror. It is a complete rewrite in homage to the once excellent jsperf.com now with hopefully a more modern & maintainable codebase.

jsperf.com URLs are mirrored at the same path, e.g:

https://jsperf.com/negative-modulo/2

Can be accessed at:

https://jsperf.app/negative-modulo/2

Test case details

Title *

Description
(Markdown syntax is allowed)

Preparation Code

Preparation HTML
(this will be inserted in the <body> of a valid HTML5 document in standards mode)
(useful when testing DOM operations or including libraries)

Setup JSconst nums = new Array(100).fill(0).map(() => new Array(100).fill(0));

Teardown JS

Test cases

Test #1

Title *

Async

Code *const bad1a = nums.reduce((acc, row) => [...acc, ...row], []);

Test #2

Title *

Async

Code *

const bad1b = nums.reduce((acc, row) => {
  row.forEach(el => acc.push(el));
  return acc;
}, []);

Test #3

Title *

Async

Code *

const bad1c = nums.reduce((acc, row) => {
  acc.push(...row);
  return acc;
}, []);

Test #4

Title *

Async

Code *

let bad2a = [];
nums.forEach((arr) => bad2a = bad2a.concat(arr));

Test #5

Title *

Async

Code *

let bad2b = [];
for (let row = 0; row < nums.length; row++) {
  bad2b = bad2b.concat(nums[row]);
}

Test #6

Title *

Async

Code *

const bad3 = JSON.parse("[" + JSON.stringify(nums).replace(/\[|\]/g, "") + "]");

Test #7

Title *

Async

Code *const good1a = nums.flat();

Test #8

Title *

Async

Code *const good1b = nums.flatMap(row => row);

Test #9

Title *

Async

Code *

const good2a = [];
nums.forEach((arr) => good2a.push(...arr));

Test #10

Title *

Async

Code *

const good2b = [];
for (let row = 0; row < nums.length; row++) {
  good2b.push(...nums[row]);
}

Test #11

Title *

Async

Code *

const good3a = [];
for (let row = 0; row < nums.length; row++) {
  for (let col = 0; col < nums[0].length; col++) {
    good3a.push(nums[row][col]);
  }
}

Test #12

Title *

Async

Code *

const good3b = new Array(nums.length * nums[0].length);
let ind = 0;
for (let row = 0; row < nums.length; row++) {
  for (let col = 0; col < nums[0].length; col++) {
    good3b[ind] = nums[row][col];
    ind++
  }
}

Test #13

Title *

Async

Code *

const good4a = [].concat.apply([], nums);

Test #14

Title *

Async

Code *const good4b = [].concat(...nums);

Test #15

Title *

Async

Code *const good4c = Array.prototype.concat.call([], ...nums);

Test #16

Title *

Async

Code *

const good5 = [];
nums.forEach(row => Array.prototype.push.apply(good5, row));

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