1️⃣1️⃣ "while" Loop

A "while" loop runs as long as its condition remains true.

let count = 1;

while (count <= 5) {
    console.log(count);
    count++;
}

Output: 1 2 3 4 5

Be careful to update the variable. This can create an infinite loop:

let count = 1;

while (count <= 5) {
    console.log(count);
}

"count" never changes, so the condition never becomes false.

1️⃣2️⃣ "do...while"

A "do...while" loop executes the code at least once, because the condition is checked after the code runs.

let count = 10;

do {
    console.log(count);
    count++;
} while (count < 5);

Output: 10

Even though "count < 5" is false, the code runs once.

Compare:
while (count < 5) {
    console.log(count);
}

The "while" loop may execute zero times.

1️⃣3️⃣ "break"

"break" immediately stops a loop.

for (let i = 1; i <= 10; i++) {
    if (i === 5) {
        break;
    }
    console.log(i);
}

Output: 1 2 3 4

1️⃣4️⃣ "continue"

"continue" skips the current iteration and moves to the next one.

for (let i = 1; i <= 5; i++) {
    if (i === 3) {
        continue;
    }
    console.log(i);
}

Output: 1 2 4 5

1️⃣5️⃣ Nested Loops

You can put one loop inside another.

for (let i = 1; i <= 3; i++) {
    for (let j = 1; j <= 2; j++) {
        console.log(i, j);
    }
}

Output:
• 1 1
• 1 2
• 2 1
• 2 2
• 3 1
• 3 2

Nested loops are useful for:
• Grids
• Tables
• Matrices
• Combinations
• Certain algorithmic problems

But they can become expensive when working with large datasets.

⭐ 1️⃣6️⃣ "for...of"

"for...of" is especially useful for iterating over values in an iterable such as an array or string.

let fruits = ["Apple", "Banana", "Mango"];

for (let fruit of fruits) {
    console.log(fruit);
}

Output: Apple Banana Mango

⭐ 1️⃣7️⃣ "for...in"

"for...in" is commonly used to iterate over enumerable property keys of an object.

let person = {
    name: "Rahul",
    age: 25,
    city: "Pune"
};

for (let key in person) {
    console.log(key);
}

Output: name age city

To access the corresponding value:
for (let key in person) {
    console.log(key, person[key]);
}

Output: name Rahul, age 25, city Pune

Important distinction
• for...of → values
• for...in → property keys

🧠 Real-World Example

Imagine an e-commerce application. You want to check whether each customer has completed their payment.

let payments = [
    "success",
    "success",
    "failed",
    "success"
];

for (let payment of payments) {
    if (payment === "success") {
        console.log("Order confirmed");
    } else {
        console.log("Payment failed");
    }
}

Output: Order confirmed, Order confirmed, Payment failed, Order confirmed

💻 Practice

1️⃣ Voting eligibility
Write a program that prints Eligible when age is 18 or above, otherwise Not eligible

2️⃣ Even numbers
Use a loop to print: 2 4 6 8 10

3️⃣ Multiplication table
Print the multiplication table of 7

4️⃣ Find a number
Loop from 1 to 20 and stop when you reach 13. Use "break".

5️⃣ Skip numbers
Loop from 1 to 10 but skip 5. Use "continue".

6️⃣ Predict the output
for (let i = 1; i <= 5; i++) {
    if (i === 3) {
        continue;
    }
    console.log(i);
}
7️⃣ Challenge
Write a program that checks numbers from 1 to 20 and prints Even for even numbers and Odd for odd numbers.
Hint: number % 2 === 0

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