A function with no return gives undefined
Name:
Date:
Class:
A
Quick Questions
Shade in the A or B circle for each question.
1. What does this code print?
function add(a, b) {
a + b;
}
console.log(add(2, 3));
2. Which function gives back a value that can be stored in a variable?
3. After this code runs, what is stored in result?
function greet() {
console.log('Hi');
}
let result = greet();
4. True or false: console.log inside a function is the same as return.
5. A function only needs to print a message on screen. Does it need a return statement?
B
Match the Pairs
Draw a line connecting each item on the left to its match on the right.
| Left column | Right column | |
|---|---|---|
| 1function add(a, b) { a + b; } console.log(add(2, 3)); | AThe result is stored in a but never returned, so undefined is printed. Add return a; at the end. | |
| 2let result = showTotal(5, 4); | Bconsole.log only prints the value, it does not return it, so answer stores undefined. Use return n * n; instead. | |
| 3A function that gives a value back to the caller must use return | Cresult holds undefined when showTotal only uses console.log and has no return | |
| 4A function that only does a job, like showing a message, can leave out return | Dfunction greet(name) { console.log('Hi ' + name); } | |
| 5function square(n) { console.log(n * n); } let answer = square(4); | EPrints undefined, because add never uses return so it gives back nothing | |
| 6function area(w, h) { let a = w * h; } console.log(area(3, 2)); | Ffunction double(n) { return n * 2; } |
C
Definitions
undefined
D
Fill in the Blanks
Complete each line of code by filling in the missing parts.
1.
function add(a, b) {
______ a + b;
}
2.
function hi() { console.log("Hi"); }
let x = hi();
console.log(x === _________);
3.
function sq(n) { ______ n * n; }
let r = sq(3);
console.log(r);
4.
function greet() { console.log("Hi"); }
let msg = _____();
console.log(msg);
5.
function sq(n) { n * n; }
let r = sq(4);
console.log(______ r);
E
Spot the Error
Shade in the letter of the line that contains an error.
Question 1
A
const sq = n => { n * n };
B
const result = sq(4);
C
console.log(result);
Question 2
A
function greet(name) {
B
const msg = 'Hi ' + name;
C
console.log(msg);
D
}
E
const text = greet('Zoe');
Question 3
A
function add(a, b) {
B
const sum = a + b;
C
return;
D
}
E
console.log(add(2, 3));
Question 4
A
function avg(a, b) {
B
const m = (a + b) / 2;
C
m;
D
}
E
console.log(avg(4, 8));
Question 5
A
function cube(n) {
B
console.log(n * n * n);
C
}
D
const c = cube(3);
Answer Key
A function with no return gives undefined
Section A: Quick Questions
Q1
A — undefined
Q2
B — function double(n) { return n * 2; }
Q3
A — undefined
Q4
A — False: console.log only shows a value, return gives it back
Q5
B — No: it does a job, so it can skip return
Section B: Match the Pairs
Q1
function add(a, b) { a + b; }
console.log(add(2, 3)); → Prints undefined, because add never uses return so it gives back nothing
Q2
let result = showTotal(5, 4); → result holds undefined when showTotal only uses console.log and has no return
Q3
A function that gives a value back to the caller must use return → function double(n) { return n * 2; }
Q4
A function that only does a job, like showing a message, can leave out return → function greet(name) { console.log('Hi ' + name); }
Q5
function square(n) {
console.log(n * n);
}
let answer = square(4); → console.log only prints the value, it does not return it, so answer stores undefined. Use return n * n; instead.
Q6
function area(w, h) {
let a = w * h;
}
console.log(area(3, 2)); → The result is stored in a but never returned, so undefined is printed. Add return a; at the end.
Section C: Definitions
Q1
undefined — The value a function gives back when it has no return statement. console.log only shows a value on screen, so a variable storing the result will hold undefined.Section D: Fill in the Blanks
Q1
function add(a, b) {
return a + b;
}Q2
function hi() { console.log("Hi"); }
let x = hi();
console.log(x === undefined);Q3
function sq(n) { return n * n; }
let r = sq(3);
console.log(r);Q4
function greet() { console.log("Hi"); }
let msg = greet();
console.log(msg);Q5
function sq(n) { n * n; }
let r = sq(4);
console.log(typeof r);Section E: Spot the Error
Q1
A — Once the arrow function has curly braces, it needs an explicit return. Without one it gives back undefined, so result holds undefined. It should be const sq = n => n * n; or { return n * n; }.
Q2
C — console.log only shows the message on screen, it does not give a value back. The function never reaches a return, so text stores undefined. Line 3 should be return msg;
Q3
C — A return with no value gives back undefined, so the call prints undefined instead of 5. It should be return sum;
Q4
C — Writing the variable name on its own line just evaluates it and throws it away. With no return keyword the function gives back undefined. It should be return m;
Q5
B — console.log shows the answer but does not return it, so cube(3) gives undefined and c stores undefined. Line 2 should be return n * n * n;