Apps are full of lists: scores, steps, names, messages. A loop repeats code once for each item, so three lines of code can handle a list of any length. A for loop with i going from 0 up to the list’s length visits positions 0, 1, 2 and so on to the last item. Inside the loop you can add up a total, count the items that pass a test, keep the biggest value or show each name in turn.
One by one — “the loop visits positions 0, 1, 2 … up to the last item”
for (let i = 0; i < list.length; i++) visits every item, from position 0.
Total: add each item. Count: add 1 when the test is true. Best: keep the biggest so far.
The body runs once per item: a list of 5 runs it 5 times.
Use it for: Adding scores, counting passes, finding high scores and showing lists of names.
Worked example: 🔁 What number does this code show?
let steps = [8, 15, 13, 9];
let total = 0;
for (let i = 0; i < steps.length; i++) {
total = total + steps[i];
}
show(total); → 45
Work it out in your head or on paper, then tap your answer — or type it and press Check. Stuck? Press “Show me how”.
Right: 0 · Tried: 0
🏁 Lesson 19 test
20 questions. Check each answer, then go to the next one. Get 16 or more right to pass.
🏅 Sign in with Google to earn the
🔁 List Loop Runner badge when you pass — and a certificate when you finish all 8 lessons of
Part 3 · Logic and Building. You can still take the test without signing in.
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