Array Iterations & Regular Expressions

forEach runs a function for each array item. It does not return a new array — use map for that.

forEach

forEach runs a function for each array item. It does not return a new array — use map for that.

Real-life example: Calling each student name from attendance sheet — read only, no new list.

forEach

["apple", "mango"].forEach((fruit, index) => {
  console.log(index, fruit);
});

map, filter, reduce

map — new array with changes. filter — new array with matches. reduce — fold all items into one value (sum, max, object).

Real-life example: reduce — add all bill amounts into one total at month end.

reduce total

const bills = [100, 250, 75];
const total = bills.reduce((sum, bill) => sum + bill, 0);
console.log(total); // 425

some and every

some — true if at least one item passes. every — true if all items pass.

Real-life example: some — at least one egg is broken. every — all eggs are fresh.

some and every

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

RegExp — patterns in text

Regular expressions match patterns in strings. Write /pattern/ or new RegExp("pattern").

Real-life example: RegExp is a stencil — only text that fits the hole shape is selected.

Create RegExp

const pattern = /hello/i; // i = ignore case
pattern.test("Hello World"); // true

test and match

test returns true/false. match returns matched parts or null.

Real-life example: test — "Does this look like an email?" match — "Show me the phone number part."

test and match

/\d+/.test("Room 42");     // true — has digits
"Price: 499".match(/\d+/);    // ["499"]

Common patterns — email and digits

Simple checks: email has @ and dot; digits use \d. Real validation needs stricter rules, but these help in learning.

Real-life example: Email pattern is a basic gate check at school entry — not full security, but catches obvious mistakes.

Do not over-trust regex alone for payments or login — always validate on server too.

Email and digits

const email = "user@rishtaara.com";
const emailOk = /^[^\s@]+@[^\s@]+\.[^\s@]+$/.test(email);

const phone = "9876543210";
const allDigits = /^\d{10}$/.test(phone);