A function is a named block of code you can use again and again. It takes inputs called parameters — in function tip(bill), bill is a parameter — and gives a value back with return. To work out what a line like show(fee(2) + fee(10)) shows, run the function once for each call, write down what each call returns, and then finish the line. Functions keep app code short and tidy.
Write once, use often — “put values in, get a result back with return”
function name(parameter) { …; return result; } — call it with name(value).
Work out each call separately, then finish the line.
Inside a function, if / return can give different results for different inputs.
Use it for: Prices, scores, greetings and any sum your app does many times.
Worked example: 🧰 A museum app works out the entry fee. What number does this code show?
function fee(age) {
if (age < 5) {
return 0;
}
return 40;
}
show(fee(2) + fee(10)); → 40
fee(2): 2 < 5, so it returns 0. fee(10): 10 is not under 5, so it returns 40.
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 20 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
🧰 Function Builder 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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