for…of, filter and map for…of, filter और map

1. The for…of loop

When you just need each value (not the index), for...of is simpler:

• for (const city of cities) { ... } — city is each item in turn
• It works on strings too: for (const ch of "Pune") gives P, u, n, e

A string method you will use here: "aeiou".includes(ch) is true when ch is a vowel.

                const snacks = ["samosa", "vada pav", "dhokla"];
for (const s of snacks) {
  console.log(`I love ${s}`);
}
              

Challenge: Counting with for…of

Using for...of loops:

1. Count the vowels (a, e, i, o, u) in city and store the count in vowels.
2. Add up the lengths of all names in cities and store it in letters.

2. filter and map

Two array methods save a lot of loops. Both take a tiny function written with an arrow =>:

• filter keeps only the items that pass a test: marks.filter(m => m >= 33) keeps the passing marks
• map changes every item and gives a new array of the same length: prices.map(p => p * 2) doubles every price

Read m => m >= 33 as “for each m, is m at least 33?”. The original array is not changed.

                const prices = [120, 450, 80, 999];
const cheap = prices.filter(p => p < 200);
const inPaise = prices.map(p => p * 100);
console.log(cheap);   // [120, 80]
console.log(inPaise); // [12000, 45000, 8000, 99900]
              

Challenge: Who passed? Add grace marks

Using the marks array:

• passed: only the marks that are 33 or more (use filter)
• withGrace: every mark plus 5 grace marks (use map)