What are JavaScript Loops? See Examples in detail

Loops in JavaScript allow you to execute a block of code multiple times, which is essential for tasks like iterating over arrays, objects, or performing repeated calculations.

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1. The for Loop

The for loop is commonly used when the number of iterations is known:

for (let i = 0; i < 5; i++) {
    console.log("Iteration:", i);
}

• i is the loop counter.
• The loop continues while the condition (i < 5) is true.
• i++ increments the counter after each iteration.

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2. The while Loop

The while loop runs as long as a condition is true:

let count = 0;
while (count < 5) {
    console.log("Count:", count);
    count++;
}

• Use while when the number of iterations is not known in advance.

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3. The do...while Loop

Executes the block at least once, then checks the condition:

let num = 0;
do {
    console.log("Number:", num);
    num++;
} while (num < 5);

• Useful when you want the code to run at least one time regardless of the condition.

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4. The for...of Loop

Simpler way to loop through arrays:

let fruits = ["apple", "banana", "mango"];
for (let fruit of fruits) {
    console.log(fruit);
}

• Iterates over values directly, not indexes.

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5. The for...in Loop

Used to iterate over object properties:

let person = {name: "Alice", age: 25, city: "New York"};
for (let key in person) {
    console.log(key + ": " + person[key]);
}

• Iterates over keys, not values directly.

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6. Break and Continue

Control loop execution:

for (let i = 0; i < 10; i++) {
    if (i === 5) break;    // Stops loop
    if (i % 2 === 0) continue; // Skips even numbers
    console.log(i);        // 1, 3
}

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7. Practical Tips

• Loops are essential for processing arrays and objects.
• Avoid infinite loops by ensuring the condition eventually becomes false.
• Use for...of for arrays and for...in for objects for cleaner code.

Mastering loops is key to automating repetitive tasks and processing data efficiently in JavaScript.

Citations:

• Learn JavaScript – Savanka
• JavaScript Tutorial – W3Schools