Comparing performance to filter items of an array in JavaScript

compare_array_filter_performance.js

// Comparing performance to filter items of an array.

// I want to convert array data, but I don't want to include some of the data.

const N = 50000;
const data = [];
for(let i=0; i<N; i++) {
  data.push(i);
}

const answer = [];
for(let i=0; i<N; i++) {
  if (i % 2 == 0) {
    answer.push(i);
  }
}
const check = (result) => {
  if (result.length !== answer.length) {
    console.log('NG');
    return;
  }

  if (!result.every((value, index) => answer[index] === value)) {
    console.log('NG');
    return;
  }

  console.log('OK');
}


// 1. map & filter
const startTime1 = new Date();
const data1 = data.map(item => {
  if (item % 2) {
    return null;
  }
  return item;
}).filter(item => item !== null);
const endTime1 = new Date();

console.log('1. map & filter: ', endTime1 - startTime1);
check(data1);


// 2. reduce
const startTime2 = new Date();
const data2 = data.reduce((arr, item) => {
  if (item % 2) {
    return arr;
  }
  return [...arr, item];
}, []);
const endTime2 = new Date();

console.log('2. reduce: ', endTime2 - startTime2);
check(data2);


// 3. forEach & push
const startTime3 = new Date();
const data3 = [];
data.forEach(item => {
  if (item % 2) {
    return;
  }
  data3.push(item);
});
const endTime3 = new Date();

console.log('3. forEach & push: ', endTime3 - startTime3);
check(data3);


// 1. map & filter:  4
// 2. reduce:  3450
// 3. forEach & push:  3