Variables: let, const, var

Declares a variable whose value can be changed later.

Part of: JavaScript Coding without HTML and CSS — Module 3, ACARA Digital Technologies Years 7–8 — Programming with Control Structures and Functions (JavaScript) — Module 8, ACARA Digital Technologies Years 9–10 — Modular and Object-Oriented Programming (JavaScript) — Module 2

Understanding Variables: let, const, var in JavaScript

What it does: var is the original keyword, now mostly replaced by let/const. Using const shows the value is meant to stay the same. let creates a variable whose value can change. const locks the value so it can't be changed. let and const are preferred over the older 'var' keyword. Redeclaring a let variable in the same scope causes an error. const signals to other developers that the value is fixed. JavaScript is case-sensitive, so it must be lowercase 'let'.

Common mistakes: 'const' is misspelled as 'cnst'. const values cannot be reassigned after they're set.

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Free printable worksheet with full answer key — or add this module to a class and your students practise it interactively.

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This module's key terms are also in a printable crossword (Modules 1–10) and word search (Modules 1–29).

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Each concept is reinforced from every angle — learned, then applied, then tested.

Learning

Duo

Can a variable declared with let be reassigned later?

YesNo

Matches

const pi = 3.14; pi = 3.15;

↓

Wrong - const variables can't be reassigned

Applying

Meanings

Term

let

Meaning

Declares a variable whose value can be changed later.

Practice

let age = 12;

Testing

Gaps

age = 12

Check Answer

Spots

1let age = 12;

2cnst name = "Sam";

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Quick Questions

1. Can a variable declared with let be reassigned later?

A. Yes ✓

B. No

let creates a variable whose value can change.

2. Can a variable declared with const be reassigned later?

A. No ✓

B. Yes

const locks the value so it can't be changed.

3. Is 'var' the modern, preferred way to declare variables?

A. Yes

B. No ✓

let and const are preferred over the older 'var' keyword.

4. Does 'let count = 5;' declare a variable named count?

A. No

B. Yes ✓

This line creates a variable called count with value 5.

5. Can you redeclare the same variable name with let twice?

A. No ✓

B. Yes

Redeclaring a let variable in the same scope causes an error.

Match the Pairs

let age = 12; → Declares a variable that can change later

const name = "Sam"; → Declares a variable that can never be reassigned

The older, less preferred way to declare variables → var total = 100;

Signals to other developers that a value is fixed → const

const pi = 3.14; pi = 3.15; → Wrong - const variables can't be reassigned

LET score = 0; → Wrong - the keyword 'let' must be lowercase

Key Term

let

Declares a variable whose value can be changed later.

Fill in the Blanks

1. let age = 12

Hint: Type the keyword used to declare a variable that can change.

2. const name = "Sam"

Hint: Type the keyword used to declare a variable that never changes.

3. let score = 0; score = score + 1

Hint: Type the operator used to add to the score.

4. var total = 100

Hint: Type the older keyword used to declare a variable.

5. const pi = 3.14

Hint: Type the keyword used to declare a variable that never changes.

Spot the Error

Question 1

A let age = 12;

B cnst name = "Sam";

C age = 13;

Line B — 'const' is misspelled as 'cnst'.

Question 2

A const pi = 3.14;

B let score = 0;

C score = score + 1;

D let count = 5;

E pi = 3.15;

Line E — const values cannot be reassigned after they're set.

Question 3

A LET total = 10;

B let count = 5;

C count = 6;

Line A — 'let' must be lowercase - a capital L causes an error.

Question 4

A var oldWay = 1;

B let modernWay = 2;

C const modernWay = 3;

Line C — You can't redeclare 'modernWay' - it's already declared with let.

Question 5

A const name = "Sam";

B let age = 12;

C age == 13;

Line C — Assignment uses a single =, not the comparison operator ==.

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