fusion-block02.js

// non-fusion approach

const data = [
  1,
  2,
  3,
  4,
  5,
];

const add = (x) => x + 1;
const multiplyBy2 = (x) => x * 2;

const res = data
  .map((i) => {
    console.log('add mapper'); // called 5 times
    return add(i);
  })
  .map((i) => {
    console.log('multiplyBy2 mapper'); // called 5 times
    return multiplyBy2(i);
  })

// [ 4, 6, 8, 10, 12 ]