Sets – Basics

Creates a new Set, a built-in object that stores only unique values.

Part of: JavaScript Coding without HTML and CSS — Module 52

Understanding Sets – Basics in JavaScript

What it does: A Set only ever keeps one copy of each unique value. add() stores "red" in the colors Set. new Set() creates an empty Set ready to store unique values. add() inserts the given value into the Set. JavaScript requires a capital S: new Set(). JavaScript is case-sensitive, so 'add' must be lowercase. Adding a duplicate simply has no effect - it isn't an error. add() inserts 1 into the Set, if it isn't already there.

Common mistakes: 'Set' must start with a capital S, not lowercase. 'add' must be lowercase - a capital A causes an error.

Class: _____________________ · Name: _____________________ · Date: _________

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 41–52) and word search (Modules 21–52).

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

Learning

Duo

Does new Set() create a new Set object?

YesNo

Matches

let s = new set();

↓

Wrong - 'Set' must start with a capital S

Applying

Meanings

Term

new Set()

Meaning

Creates a new Set, a built-in object that stores only unique values.

Practice

let nums = new Set();

Testing

Gaps

let nums = Set();

Check Answer

Spots

1let s = new set();

2s.add(1);

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Quick Questions

1. Does new Set() create a new Set object?

A. No

B. Yes ✓

new Set() creates an empty Set ready to store unique values.

2. Does add() add a value to a Set?

A. Yes ✓

B. No

add() inserts the given value into the Set.

3. Does a Set automatically remove duplicate values?

A. No

B. Yes ✓

A Set only ever stores one copy of each unique value.

4. Is 'set' with a lowercase s valid for creating a Set?

A. No ✓

B. Yes

JavaScript requires a capital S: new Set().

5. Must 'add' be written in lowercase?

A. Yes ✓

B. No

JavaScript is case-sensitive, so 'add' must be lowercase.

Match the Pairs

new Set() → Creates a new, empty Set

nums.add(1) → Adds the value 1 to the nums Set

Automatically removes duplicate values from a collection → Set

Inserts a value into a Set → colors.add("red")

let s = new set(); → Wrong - 'Set' must start with a capital S

s.Add(1); → Wrong - 'add' must start with a lowercase a

Key Term

new Set()

Creates a new Set, a built-in object that stores only unique values.

Fill in the Blanks

1. let nums = new Set();

Hint: Type the keyword used to create a new Set.

2. nums.add(1);

Hint: Type the method that adds a value to a Set.

3. let colors = new Set();

Hint: Type the keyword used to create a new Set.

4. colors.add("red");

Hint: Type the method that adds a value to a Set.

5. nums.add(2);

Hint: Type the method that adds a value to a Set.

Spot the Error

Question 1

A let s = new set();

B s.add(1);

C console.log(s);

Line A — 'Set' must start with a capital S, not lowercase.

Question 2

A let s2 = new Set();

B s2.Add(2);

C console.log(s2);

Line B — 'add' must be lowercase - a capital A causes an error.

Question 3

A let s3 = new Set();

B s3.add(3);

C s3.add(3);

Line C — This line is actually correct - adding a duplicate just has no effect.

Question 4

A let a = 1;

B let b = 2;

C let s5 = new set();

Line C — 'Set' must start with a capital S, not lowercase.

Question 5

A let s6 = new Set();

B s6.add(4);

C console.log(s6);

D s6.Add(5);

Line D — 'add' must be lowercase - a capital A causes an error.

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