How to Write a For Loop in JavaScript

JavaScript offers several types of for loops for different use cases.

Traditional For Loop

The classic C-style for loop:

for (let i = 0; i < 5; i++) {
  console.log(i);
}
// Output: 0, 1, 2, 3, 4

For…of Loop (ES6+)

Iterate over iterable objects like arrays and strings:

const fruits = ["apple", "banana", "cherry"];

for (const fruit of fruits) {
  console.log(fruit);
}
// Output: apple, banana, cherry

// Works with strings too
for (const char of "hello") {
  console.log(char);
}

For…in Loop

Iterate over object properties:

const person = { name: "Alice", age: 25, city: "Paris" };

for (const key in person) {
  console.log(`${key}: ${person[key]}`);
}
// Output:
// name: Alice
// age: 25
// city: Paris

forEach() Method

Array method for iteration:

const numbers = [1, 2, 3, 4, 5];

numbers.forEach((num, index) => {
  console.log(`Index ${index}: ${num}`);
});

Looping with Index

Get both index and value:

const fruits = ["apple", "banana", "cherry"];

// Traditional for loop
for (let i = 0; i < fruits.length; i++) {
  console.log(`${i}: ${fruits[i]}`);
}

// Using entries()
for (const [index, fruit] of fruits.entries()) {
  console.log(`${index}: ${fruit}`);
}

Break and Continue

Control loop execution:

// Break - exit the loop
for (let i = 0; i < 10; i++) {
  if (i === 5) break;
  console.log(i); // 0, 1, 2, 3, 4
}

// Continue - skip iteration
for (let i = 0; i < 5; i++) {
  if (i === 2) continue;
  console.log(i); // 0, 1, 3, 4
}

Summary

• Use traditional for when you need the index or complex conditions
• Use for…of to iterate over array values (recommended for arrays)
• Use for…in to iterate over object properties
• Use forEach() for functional-style iteration