Reading user input with prompt()

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Quick Questions

Shade in the A or B circle for each question.

1. Which line stores what the user types in a variable called name?

A let name = prompt("Your name?");

B prompt("Your name?") = name;

2. A user types 14 into prompt("Age?"). What data type does prompt() return?

A A number: 14

B A string: "14"

3. What does prompt("Favourite subject?") do when it runs?

A Shows a message box, waits for typing and returns the text

B Prints the message in the console and carries on straight away

4. What does prompt() return if the user clicks Cancel?

A An empty number 0

B null

5. let a = prompt("First?"); with the user typing 5 and then 3 in a second prompt stored in b. What does a + b give?

A "53" because both are strings

B 8 because they are numbers

Match the Pairs

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

Left column		Right column
1let name = prompt("Your name?");		Aa is a string, so a + 5 joins text instead of adding. If the user types 3 the result is "35". Use Number(prompt(...)).
2let age = prompt("Your age?"); console.log(typeof age);		Bif (answer === null) { console.log("Cancelled"); }
3prompt() returns null when the user presses Cancel, so you can check for it		CShows a message box, waits for the user to type, and stores what they typed in the variable name
4Input is a string, so convert it with Number() before doing maths		Dlet n = Number(prompt("Pick a number"));
5prompt("Your name?"); console.log("Hi " + name);		EPrints string, because prompt() always returns text, even when the user types digits
6let a = prompt("First number?"); let total = a + 5;		FThe answer was never stored in a variable, so name does not exist. Use let name = prompt("Your name?");

Definitions

prompt("question")

Fill in the Blanks

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

let name = ______("What is your name?");

let name = prompt("Your name?"); console.log("Hi " + ____);

let age = prompt("Age?"); console.log(______ age);

let name = prompt("Your name?"); if (name === ____) { console.log("Cancelled"); }

let num = ______(prompt("Enter a number:"));

Spot the Error

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

Question 1

A // ask for a name

B let name = promt("Name?");

C console.log("Hi " + name);

Question 2

A let age = prompt("Age?");

B let next = Number(age) + 1;

C console.log("Next: " + nex);

Question 3

A let n = prompt("Number?");

B let total = Number(n) + 5;

C console.log("Total: " + total;

Question 4

A let ans = prompt("Number?");

B let n = Number(ans);

C let total = n + 5;

D console.log("Sum:", ans + 5);

Question 5

A let city = prompt(City?);

B console.log("Hello " + city);

C console.log(city.length);

Answer Key

Reading user input with prompt()

Section A: Quick Questions

A — let name = prompt("Your name?");

B — A string: "14"

A — Shows a message box, waits for typing and returns the text

B — null

A — "53" because both are strings

Section B: Match the Pairs

let name = prompt("Your name?"); → Shows a message box, waits for the user to type, and stores what they typed in the variable name

let age = prompt("Your age?"); console.log(typeof age); → Prints string, because prompt() always returns text, even when the user types digits

prompt() returns null when the user presses Cancel, so you can check for it → if (answer === null) { console.log("Cancelled"); }

Input is a string, so convert it with Number() before doing maths → let n = Number(prompt("Pick a number"));

prompt("Your name?"); console.log("Hi " + name); → The answer was never stored in a variable, so name does not exist. Use let name = prompt("Your name?");

let a = prompt("First number?"); let total = a + 5; → a is a string, so a + 5 joins text instead of adding. If the user types 3 the result is "35". Use Number(prompt(...)).

Section C: Definitions

prompt("question") — Shows a message box, waits for the user to type, then returns what they typed as a string. Store it in a variable. Cancel returns null.

Section D: Fill in the Blanks

let name = prompt("What is your name?");

let name = prompt("Your name?");
console.log("Hi " + name);

let age = prompt("Age?");
console.log(typeof age);

let name = prompt("Your name?");
if (name === null) {
  console.log("Cancelled");
}

let num = Number(prompt("Enter a number:"));

Section E: Spot the Error

B — The function name is misspelled. It must be prompt, with the letter p before t, otherwise JavaScript throws a ReferenceError.

C — The variable is called next, but this line uses nex, which was never declared. It should be next.

C — The closing bracket of console.log( is missing. It should end with total);

D — prompt() always returns a string, so ans + 5 joins the text, for example "35" instead of 8. Use the converted number: total (or n + 5).

A — The question inside prompt() is text, so it needs quotation marks: prompt("City?").