functional & declarative

functional_declarative.js

let sum = 0;
let numbers = [2, 4, 6, 10, 16];

for (let i = 0; i < numbers.length; i++) {
  numbers[i] = numbers[i] - 1;
  if (numbers[i] % 3 === 0) {
    sum += numbers[i];
  }
}
console.log("0", sum);
numbers = [2, 4, 6, 10, 16];

let reduced = numbers.map((n) => n - 1);
let divisible = reduced.filter((n) => n % 3 === 0);
sum = divisible.reduce((acc, n) => acc + n, 0);
console.log("1:", sum);

sum = numbers
  .map((n) => n - 1)
  .filter((n) => n % 3 === 0)
  .reduce((acc, n) => acc + n, 0);
console.log("2:", sum);

const subtractOne = (n) => n - 1;
const isDivisibleBy3 = (n) => n % 3 === 0;
const add = (acc, n) => acc + n;
sum = numbers.map(subtractOne).filter(isDivisibleBy3).reduce(add, 0);
console.log("3:", sum);

const users = [
  { name: "alice", id: 0 },
  { name: "bob", id: 2 },
];
// curried function
const byId = (id) => {
  return (item) => {
    return item.id === id;
  };
};
// const byId = (id) => (item) => item.id === id; // one line
console.log(users.find(byId(2) /*** partially apply id to 2 ***/));