Loops: Repeating Actions

Loops let you repeat code without copy-pasting it, essential once you need to process more than a handful of items.

for (let i = 1; i <= 5; i++) {
  console.log("Lesson " + i);
}

let scores = [80, 92, 67, 100];
for (const s of scores) {
  console.log(s);
}

for loops

A classic for (init; condition; increment) loop: let i = 1 runs once at the start, i <= 5 is checked before every pass, i++ runs after every pass. Together they count from 1 to 5, printing a line each time.

for...of loops

for (const s of scores) visits every element in an array directly, no counter needed, use it whenever you don't care about the index, just each value.

while loops

let attempts = 0;
while (attempts < 3) {
  console.log("Attempt " + (attempts + 1));
  attempts++;
}

A while (condition) { ... } loop keeps running as long as condition stays true, checked before every pass. Unlike for, nothing about a while loop's structure guarantees it'll ever stop, forgetting to update attempts here would loop forever, always make sure something inside the loop moves it toward false.