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Lesson · Chapter: For Loops+10 XP for reading

Looping with For

The for loop is a compact way to repeat things a specific number of times.

The Three Parts

A for loop packs the counter setup, the condition, and the update into one line:

javascript
for (let i = 0; i < 5; i++) {
console.log("Hello!");
}
Output
Press Run to see the output.

This prints Hello! five times. The three parts, separated by semicolons:

  1. let i = 0 — start the counter at 0
  2. i < 5 — keep looping while this is true
  3. i++ — add 1 to the counter after each round

The variable i counts 0, 1, 2, 3, 4.

Counting from 1

Start and stop wherever you like:

javascript
for (let i = 1; i <= 5; i++) {
console.log(i);
}
Output
Press Run to see the output.

Output:

1
2
3
4
5

Counting by Steps

Change the update part to count by any amount:

javascript
for (let i = 2; i <= 10; i += 2) {
console.log(i);
}
Output
Press Run to see the output.

Output:

2
4
6
8
10

To count backwards, use i--:

javascript
for (let i = 3; i >= 1; i--) {
console.log(i);
}
Output
Press Run to see the output.

Looping Over Strings

Use for...of to visit each character in a string:

javascript
for (let letter of "Hello") {
console.log(letter);
}
Output
Press Run to see the output.

Output:

H
e
l
l
o

Looping Over Arrays

for...of works on arrays too (more on arrays soon!):

javascript
let colors = ["red", "blue", "green"];
for (let color of colors) {
console.log(color);
}
Output
Press Run to see the output.

For vs While

Use for when you know how many times to loop. Use while when you don't know in advance.