Iteration Methods in Javascript

Here’s a short and easy way to remember JavaScript array methods:

🔹 Iteration Methods

1. forEach → Runs a function on each item (No return).

    [1, 2, 3].forEach(num => console.log(num));
   

2. map → Creates a new array by transforming each item.

    const squared = [1, 2, 3].map(num => num * num); // [1, 4, 9]
   

3. filter → Creates a new array with items that pass a condition.

    const evens = [1, 2, 3, 4].filter(num => num % 2 === 0); // [2, 4]
   

4. reduce → Reduces an array to a single value.

    const sum = [1, 2, 3, 4].reduce((acc, num) => acc + num, 0); // 10
   

🔹 Checking Methods

5. some → Returns true if at least one item meets a condition.

    [1, 2, 3].some(num => num > 2); // true
   

6. every → Returns true if all items meet a condition.

    [1, 2, 3].every(num => num > 0); // true
   

🔹 Finding Methods

7. find → Returns first matching item.

    [1, 2, 3, 4].find(num => num > 2); // 3
   

8. findIndex → Returns index of the first matching item.

    [1, 2, 3, 4].findIndex(num => num > 2); // 2
   

🔹 Sorting Methods

9. sort → Sorts array (modifies original!).

    [3, 1, 4].sort((a, b) => a - b); // [1, 3, 4]
   

🔹 Conversion Methods

10. toString → Converts array to a string.

[1, 2, 3].toString(); // "1,2,3"

11. join → Joins array items into a string with a separator.

[1, 2, 3].join('-'); // "1-2-3"

🔹 Modifying Methods

12. slice → Extracts part of an array (does not modify original).

[1, 2, 3, 4].slice(1, 3); // [2, 3]

13. splice → Adds/removes items (modifies original).

const arr = [1, 2, 3];  
arr.splice(1, 1, 99); // [1, 99, 3]

🔹 Index Methods

14. indexOf → Finds first index of a value.

[1, 2, 3, 2].indexOf(2); // 1

15. lastIndexOf → Finds last index of a value.

[1, 2, 3, 2].lastIndexOf(2); // 3

🔹 Flattening Method

16. flat → Flattens nested arrays.

[1, [2, [3]]].flat(2); // [1, 2, 3]