Devlog - 2026-02-05

🚀 What I Did

• Theory.

🧠 What I Learned

Higher Order Functions

• Higher order functions make code more flexible and reusable.

Map

• Map method creates new array by applying a given function to each original array.

const numbers = [3, 4, 5, 6, 7].map((element, index) => {
  console.log("Element:", element);
  console.log("Index:", index);
  return element * 2;
});

• Removing a specific element from an array is not a correct way to use map.
• Current element, its index and the original array - arguments for map.

filter()

• Is used to create a new array with elements that pass a specified test.
• Returns an empty array if no elements in array pass the test.

const numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
const evenNumbers = numbers.filter((num) => num % 2 === 0);

console.log(evenNumbers); // [2, 4, 6, 8, 10]

reduce()

• reduce method allows to process an array and condense into a single value.

const numbers = [1, 2, 3, 4, 5];
const sum = numbers.reduce(
  (accumulator, currentValue) => accumulator + currentValue,
  0
);

console.log(sum); // 15

Method chaining

• A technique where you call several methods one after another.

const result = "  Hello, World!  "
  .trim()
  .toLowerCase()
  .replace("world", "JavaScript");

console.log(result); // "hello, JavaScript!"

sort()

• Used to arrange the elements of an array and returns a reference to the sorted array.

const numbers = [414, 200, 5, 10, 3];
numbers.sort();

console.log(numbers); // [10, 200, 3, 414, 5]

every() and sum()

• every - tests whether all elements in an array pass a test implemented by a provided function.

const numbers = [2, 4, 6, 8, 10];
const hasAllEvenNumbers = numbers.every((num) => num % 2 === 0);

console.log(hasAllEvenNumbers); // true

• some() - checks if at least one element passes the test.

const numbers = [1, 3, 5, 7, 8, 9];
const hasSomeEvenNumbers = numbers.some((num) => num % 2 === 0);

console.log(hasSomeEvenNumbers); // true

🔥 What’s Next

• Practice problems.
• Theory.
• Codewars.

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