JavaScript Loops: For, While, and Do-While

Understanding Loops in JavaScript

Loops are used to execute a block of code repeatedly until a specified condition is met. The most common types of loops in JavaScript are for, while, and do-while.

Example 1: For Loop

// for loop
// for(initialization; condition; increment/decrement) {
//     // code to be executed
// }
 
for(let i = 1; i <= 10; i++) {
    console.log(i);
}

This for loop initializes i to 1 and increments it by 1 until it reaches 10, logging each value of i to the console.

Example 2: Iterating Over an Array

let food = ["Burger", "Momos", "Roti", "Sabji", "Salad"];
for(let i = food.length - 1; i >= 0; i--) {
    console.log(food[i]);
}   

This loop iterates over the food array in reverse order, logging each food item to the console.

Example 3: Nested Loops

for(let i = 1; i <= 5; i++) {
    for(let j = 1; j <= 5; j++) {
        console.log(`Outer: ${i} Inner: ${j}`);
    }
}

This example demonstrates nested loops, where the inner loop runs completely for each iteration of the outer loop.

Break and Continue Statements

The break statement terminates the loop, while the continue statement skips the current iteration and moves to the next one.

// Break example
for(let i = 1; i <= 10; i++) {
    if(i == 5) {
        break;
    }
    console.log(i);
}
 
// Continue example
for(let i = 1; i <= 10; i++) {
    if(i == 5) {
        continue;
    }
    console.log(i);
}

In the first loop, when i equals 5, the loop terminates. In the second loop, when i equals 5, that iteration is skipped.

Example 4: While Loop

let i = 1;
while(i <= 10) {
    if(i == 4) {
        i++;
        continue;
    }
    console.log(i);
    i++;
}

This while loop continues to execute as long as i is less than or equal to 10. If i equals 4, that iteration is skipped.

Example 5: Do-While Loop

let i = 6;
do {
    console.log(i);
    i++;
} while(i <= 5);

The do-while loop executes the block of code at least once before checking the condition. In this case, it will log 6 and then exit since the condition is not met.