Functions calling other functions

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Quick Questions

Shade in the A or B circle for each question.

1. Can a function call another function inside its body?

A Yes. A function body can contain calls to other functions.

B No. Only code outside functions can call functions.

2. Which function is a helper function? function square(n) { return n * n; } function area(side) { return square(side); }

A square, because area calls it to do a small job

B area, because it has a longer name

3. Which design follows 'one job per function'?

A getTotal() adds the prices and showTotal() prints the result

B doEverything() adds prices, prints, asks for input and checks errors

4. A helper function returns a value. How does the calling function get that value?

A helper(5) = result;

B let result = helper(5);

5. Which function body correctly calls the helper double()?

A function quadruple(n) { return double double n; }

B function quadruple(n) { return double(double(n)); }

Match the Pairs

Draw a line connecting each item on the left to its match on the right.

Left column		Right column
1function area(w, h) { return w * h; }		Afunction total(a, b) { return double(a) + double(b); }
2function showArea(w, h) { console.log(area(w, h)); }		BA small helper function that does one job: it returns the area of a rectangle.
3A helper function returns a value, and the calling function uses that value in a calculation.		Cfunction main() { greet(); playGame(); sayBye(); }
4A main program calls several small functions in order, one job each.		DA function that calls the helper area() inside its body and prints the result.
5function showArea(w, h) { console.log(area); }		EThe helper area() has no return, so it gives back undefined and showArea prints undefined.
6function area(w, h) { w * h; } function showArea(w, h) { console.log(area(w, h)); }		FThe helper is named but never called. It needs brackets and arguments: area(w, h).

Definitions

helper function

Fill in the Blanks

Complete each line of code by filling in the missing parts.

function twice(n) { return n * 2; } function four(n) { return _____(twice(n)); }

function isEven(n) { return n % 2 === 0; } function show(n) { console.log(______(n)); }

let name = getName(); let msg = makeGreeting(name); showMessage(___);

function sumTwice(a, b) { ______ twice(a) + twice(b); }

function entry(age) { __ (isAdult(age)) { console.log("In"); } }

Spot the Error

Shade in the letter of the line that contains an error.

Question 1

A function square(n) {

B return n * n;

C }

D function sumSquares(a, b {

E return square(a) + square(b);

F }

Question 2

A function getName() {

B console.log("Sam");

C }

D function welcome() {

E console.log("Hi " + getName());

F }

Question 3

A function area(w h) {

B return w * h;

C }

D function showArea(w, h) {

E console.log(area(w, h));

F }

Question 4

A function sq(n) {return n*n;}

B function sumSq(a, b) {

C return sq(a + b);

D }

Question 5

A function big(n) {return n>9;}

B function check(n) {

C if (big) {

D console.log("Big");

E }

F }

Answer Key

Functions calling other functions

Section A: Quick Questions

A — Yes. A function body can contain calls to other functions.

A — square, because area calls it to do a small job

A — getTotal() adds the prices and showTotal() prints the result

B — let result = helper(5);

B — function quadruple(n) { return double(double(n)); }

Section B: Match the Pairs

function area(w, h) { return w * h; } → A small helper function that does one job: it returns the area of a rectangle.

function showArea(w, h) { console.log(area(w, h)); } → A function that calls the helper area() inside its body and prints the result.

A helper function returns a value, and the calling function uses that value in a calculation. → function total(a, b) { return double(a) + double(b); }

A main program calls several small functions in order, one job each. → function main() { greet(); playGame(); sayBye(); }

function showArea(w, h) { console.log(area); } → The helper is named but never called. It needs brackets and arguments: area(w, h).

function area(w, h) { w * h; } function showArea(w, h) { console.log(area(w, h)); } → The helper area() has no return, so it gives back undefined and showArea prints undefined.

Section C: Definitions

helper function — A small function that does one job and is called from inside another function, so a big task is built from small, reusable parts.

Section D: Fill in the Blanks

function twice(n) { return n * 2; }
function four(n) { return twice(twice(n)); }

function isEven(n) { return n % 2 === 0; }
function show(n) { console.log(isEven(n)); }

let name = getName();
let msg = makeGreeting(name);
showMessage(msg);

function sumTwice(a, b) {
  return twice(a) + twice(b);
}

function entry(age) {
  if (isAdult(age)) { console.log("In"); }
}

Section E: Spot the Error

D — The closing bracket after the parameter list is missing. It should be function sumSquares(a, b) {. The function can then call the square() helper twice.

B — A helper that gives a value to another function must use return. console.log only prints, so getName() gives back undefined and welcome() prints Hi undefined. It should be return "Sam";

A — Parameters must be separated by a comma. It should be function area(w, h) {. Then showArea can call area() as a helper.

C — The helper sq() must be called on each number separately and the results added. sq(a + b) adds first and then squares, which gives a different answer. It should be return sq(a) + sq(b);

C — The helper must be called with brackets and an argument. Without them, big is just the function itself and is always truthy. It should be if (big(n)) {