Functions – Default Parameters

Assigns a default value to a parameter, used only when no argument is passed for it.

Part of: JavaScript Coding without HTML and CSS — Module 41, ACARA Digital Technologies Years 9–10 — Modular and Object-Oriented Programming (JavaScript) — Module 15

Understanding Functions – Default Parameters in JavaScript

What it does: This is exactly what a default parameter does. Passing "Sam" replaces the default "Guest" value. If no argument is given, the default value is used instead. Default parameters use = directly in the parameter list. JavaScript uses =, not :, for default parameters. Any argument passed in takes priority over the default. Parameters are declared without let or const. Default values can be any valid JavaScript expression.

Common mistakes: Default parameters use =, not ==, to assign the value. Default parameters use =, not :, to assign the value.

Class: _____________________ · Name: _____________________ · Date: _________

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

🖨 Print worksheet + answer key Add Functions – Default Parameters to a class →

This module's key terms are also in a printable crossword (Modules 41–52) and word search (Modules 21–52).

Take this worksheet further — free with Cloodit

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

Learning

Duo

Does a default parameter provide a fallback value when no argument is passed?

YesNo

Matches

function add(a, b == 0) { ... }

↓

Wrong - default parameters use =, not ==

Applying

Meanings

Term

Meaning

Assigns a default value to a parameter, used only when no argument is passed for it.

Practice

function greet(name = "Guest") {

Testing

Gaps

function greet(name "Guest") {

Check Answer

Spots

1function add(a, b == 0) {

2console.log(a + b);

Cloodit turns curriculum-aligned coding content into journeys students work through one biome at a time.

Students earn collectable badges

Over 100 of them, across seven natural biomes.

Study Buddy

Students build a real study resource

Turns their work into revision material ready for Flash Cards and Exam study.

Diamond Dash — one of Cloodit's live, competitive Sprint games

Students lock in with Sprints

Live, competitive practice for the start of the lesson or a teacher-led lesson finisher.

A Cloodit certificate of achievement, ready to personalise and print

Custom printable certificates

Honour your top performers, or encourage a student who's trying hard — ready to print in seconds.

Add to class →

Quick Questions

1. Does a default parameter provide a fallback value when no argument is passed?

A. Yes ✓

B. No

If no argument is given, the default value is used instead.

2. Is = used to assign a default value to a parameter?

A. Yes ✓

B. No

Default parameters use = directly in the parameter list.

3. Is ':' a valid way to assign a default parameter value?

A. Yes

B. No ✓

JavaScript uses =, not :, for default parameters.

4. Does passing an argument override a parameter's default value?

A. No

B. Yes ✓

Any argument passed in takes priority over the default.

5. Should 'let' be added before a parameter name in the list?

A. No ✓

B. Yes

Parameters are declared without let or const.

Match the Pairs

function greet(name = "Guest") { ... } → Uses "Guest" as name if no argument is passed

function add(a, b = 0) { ... } → Uses 0 as b if no argument is passed for b

Provides a fallback value when no argument is given → name = "Guest"

Overrides the default value when an argument is passed → greet("Sam")

function add(a, b == 0) { ... } → Wrong - default parameters use =, not ==

function mul(a, b: 1) { ... } → Wrong - default parameters use =, not :

Key Term

=

Assigns a default value to a parameter, used only when no argument is passed for it.

Fill in the Blanks

1. function greet(name = "Guest") {

Hint: Type the symbol used to assign a default value to name.

2. function add(a, b = 0) {

Hint: Type the symbol used to assign a default value to b.

3. function power(base, exp = 2) {

Hint: Type the default value used for exp.

4. function counter(step = 1) {

Hint: Type the symbol used to assign a default value to step.

5. function scale(factor = 5) {

Hint: Type the default value used for factor.

Spot the Error

Question 1

A function add(a, b == 0) {

B console.log(a + b);

C }

Line A — Default parameters use =, not ==, to assign the value.

Question 2

A function mul(a, b: 1) {

B console.log(a * b);

C }

Line A — Default parameters use =, not :, to assign the value.

Question 3

A console.log("hi");

B function greet(n "Al") {

C console.log(n);

Line B — Default parameters need an = before the value.

Question 4

A console.log("go");

B function power(let x = 2) {

C console.log(x);

Line B — Don't add 'let' inside the parameter list.

Question 5

A let a = 1;

B console.log(a);

C Function timer(s = 30) {

D console.log(s);

Line C — 'function' must be lowercase - a capital F causes an error.

Student with a class code? Join your class →