const for values that never change

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Quick Questions

Shade in the A or B circle for each question.

1. Which line correctly declares a value that should never change?

A const MAX_SCORE = 100;

B MAX_SCORE const = 100;

2. What happens when this code runs? const maxLives = 3; maxLives = 2;

A maxLives becomes 2 with no error

B TypeError: Assignment to constant variable

3. Which variable is best declared with const?

A The player's current score

B The number of days in a week

4. Which variable is best declared with let?

A let lives = 3; (it goes down when the player loses a life)

B const lives = 3; (it goes down when the player loses a life)

5. True or false: a const must be given its value when it is declared.

A True: const PI = 3.14;

B False: const PI; can be given a value later

Match the Pairs

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

Left column		Right column
1const MAX_SCORE = 100;		AMAX_SCORE is a const, so it cannot be reassigned. This causes a TypeError: Assignment to constant variable.
2let lives = 3;		BCreates a fixed value called MAX_SCORE that is set once and cannot be changed later
3Use const for a value that should never change, like the number of rounds in a game		Cconst ROUNDS = 5;
4Use let for a value that will change as the program runs, like a player's score		DCreates a variable that can be given a new value later, such as when a life is lost
5const MAX_SCORE = 100; MAX_SCORE = 200;		Etotal needs to change, but const does not allow reassignment. It should be declared with let instead.
6const total = 0; total = total + 10;		Flet score = 0;

Definitions

const

Fill in the Blanks

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

_____ MAX_SCORE = 100;

___ lives = 3; // this value will change

const TAX = 10; console.log(5 * ___);

const LIVES = 3; LIVES = 2; // _________

_____ SCHOOL_YEARS = 6; // never changes

Spot the Error

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

Question 1

A const MAX_SCORE = 100;

B let score = 90;

C score += 15;

D MAX_SCORE = score;

Question 2

A const PI = 3.14;

B const radius = 5;

C radius = radius * 2;

D console.log(PI * radius);

Question 3

A const TAX = 0.1;

B let price = 50;

C const total;

D console.log(total);

Question 4

A const MAX_LIVES = 3;

B let lives = MAX_LIVES;

C MAX_LIVES--;

D console.log(lives);

Question 5

A cosnt MAX_PLAYERS = 4;

B let joined = 2;

C console.log(MAX_PLAYERS - joined);

Answer Key

const for values that never change

Section A: Quick Questions

A — const MAX_SCORE = 100;

B — TypeError: Assignment to constant variable

B — The number of days in a week

A — let lives = 3; (it goes down when the player loses a life)

A — True: const PI = 3.14;

Section B: Match the Pairs

const MAX_SCORE = 100; → Creates a fixed value called MAX_SCORE that is set once and cannot be changed later

let lives = 3; → Creates a variable that can be given a new value later, such as when a life is lost

Use const for a value that should never change, like the number of rounds in a game → const ROUNDS = 5;

Use let for a value that will change as the program runs, like a player's score → let score = 0;

const MAX_SCORE = 100; MAX_SCORE = 200; → MAX_SCORE is a const, so it cannot be reassigned. This causes a TypeError: Assignment to constant variable.

const total = 0; total = total + 10; → total needs to change, but const does not allow reassignment. It should be declared with let instead.

Section C: Definitions

const — Declares a variable whose value is set once and cannot be reassigned. Use it for fixed values like a maximum score. Changing it later causes a TypeError.

Section D: Fill in the Blanks

const MAX_SCORE = 100;

let lives = 3; // this value will change

const TAX = 10; console.log(5 * TAX);

const LIVES = 3; LIVES = 2; // TypeError

const SCHOOL_YEARS = 6; // never changes

Section E: Spot the Error

D — MAX_SCORE was declared with const, so it cannot be reassigned. This causes a TypeError. The line should cap the score: score = MAX_SCORE;

B — radius changes on the next line, so it must be declared with let. With const, radius = radius * 2 would cause a TypeError. It should be let radius = 5;

C — A const must be given its value when it is declared, because it can never be assigned later. It should be const total = price + price * TAX;

C — MAX_LIVES is a const, so it cannot be changed with --. This causes a TypeError. The changing variable lives should be reduced: lives--;

A — The keyword const is misspelled as cosnt. JavaScript does not recognise it, so it is a syntax error. It should be const MAX_PLAYERS = 4;