JS108 - Loops & Iteration

Loops allow you to repeat actions and process lists of data efficiently.
JavaScript provides several loop types, each with different use cases.

for Loop

The classic for loop runs a block of code a specific number of times.

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

while Loop

Runs as long as the condition is true.

let n = 0;
 
while (n < 3) {
  console.log("n is " + n);
  n++;
}

do-while Loop

Runs at least once even if the condition is false.

let x = 5;
 
do {
  console.log(x);
  x--;
} while (x > 0);

for...of Loop

Used for iterating over arrays or iterable objects.

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

forEach Method

A cleaner way to loop through arrays.

fruits.forEach(function(item) {
  console.log(item);
});

With arrow functions:

fruits.forEach(item => console.log(item));

Looping Through Objects

Objects are not directly iterable.
Use for...in to loop through keys.

let user = {
  name: "Emre",
  age: 30,
  city: "Antalya"
};
 
for (let key in user) {
  console.log(key + ": " + user[key]);
}

Breaking and Continuing Loops

for (let i = 0; i < 10; i++) {
  if (i === 5) break;
  console.log(i);
}

continue skips to the next iteration:

for (let i = 0; i < 5; i++) {
  if (i === 2) continue;
  console.log(i);
}

Infinite Loops (Avoid)

A loop runs forever if the condition never becomes false.

while (true) {
  // This never stops!
}

Always ensure loop conditions update correctly.

Summary

In this lesson, you learned:

• for, while, and do-while loops
• for...of and for...in
• forEach array iteration
• How to break and continue loops
• How to avoid infinite loops

In the next lesson, we will learn DOM Manipulation — how JavaScript interacts with HTML elements.