Arrays – Creation and Indexing

Creates an array and, when placed after a variable name, accesses an element by its index.

Part of: JavaScript Coding without HTML and CSS — Module 22, ACARA Digital Technologies Years 9–10 — Modular and Object-Oriented Programming (JavaScript) — Module 22

Understanding Arrays – Creation and Indexing in JavaScript

What it does: Since indexing starts at 0, index 1 is the second element. JavaScript arrays are zero-based, so 0 is the first index. Square brackets create a new array. Arrays use square brackets [], not curly braces. Values inside an array are separated by commas. Every [ used for indexing needs a matching ]. Index 0 always refers to the first element in an array. Accessing an array element requires [ ], not ( ).

Common mistakes: Arrays use square brackets [], not round brackets (). Index access uses square brackets, not round brackets.

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This module's key terms are also in a printable crossword (Modules 11–25) and crossword (Modules 21–30) and word search (Modules 1–29) 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 [] create an array in JavaScript?

YesNo

Matches

let a = (1, 2, 3);

↓

Wrong - arrays use square brackets, not round brackets

Applying

Meanings

Term

[]

Meaning

Creates an array and, when placed after a variable name, accesses an element by its index.

Practice

let fruits = ["apple", "banana", "cherry"];

Testing

Gaps

let fruits = "apple", "banana";

Check Answer

Spots

1let a = (1, 2, 3);

2console.log(a[0]);

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Quick Questions

1. Does [] create an array in JavaScript?

A. No

B. Yes ✓

Square brackets create a new array.

2. Is the first element of an array at index 0?

A. No

B. Yes ✓

Array indexing is zero-based, so the first item is at index 0.

3. Is () used to access an element by index?

A. No ✓

B. Yes

Square brackets [], not round brackets, access array elements.

4. Does fruits[1] access the second element of the array?

A. Yes ✓

B. No

Since indexing starts at 0, index 1 is the second element.

5. Are curly braces {} used to create an array?

A. No ✓

B. Yes

Arrays use square brackets [], not curly braces.

Match the Pairs

["apple", "banana", "cherry"] → Creates an array holding three string values

fruits[0] → Accesses the first element of the fruits array

Accesses the second element of an array → colors[1]

The starting index for the first element in an array → 0

let a = (1, 2, 3); → Wrong - arrays use square brackets, not round brackets

console.log(fruits(0)); → Wrong - index access uses square brackets, not round brackets

Key Term

[]

Creates an array and, when placed after a variable name, accesses an element by its index.

Fill in the Blanks

1. let fruits = ["apple", "banana"];

Hint: Type the symbol that opens an array.

2. console.log(fruits[0]);

Hint: Type the symbol that opens an index access.

3. let colors = ["red", "blue"]; console.log(colors[1]);

Hint: Type the symbol that opens an index access.

4. let nums = [1, 2, 3]; console.log(nums[0]);

Hint: Type the index number of the first element.

5. let sizes = [10, 20, 30]; console.log(sizes[2]);

Hint: Type the index number of the third element.

Spot the Error

Question 1

A let a = (1, 2, 3);

B console.log(a[0]);

C let b = [4, 5];

Line A — Arrays use square brackets [], not round brackets ().

Question 2

A let c = [1, 2, 3];

B console.log(c(0));

C let d = [4, 5];

Line B — Index access uses square brackets, not round brackets.

Question 3

A console.log(names{0});

B let names = ["Amy", "Bob"];

C console.log(names[1]);

Line A — Index access uses square brackets, not curly braces.

Question 4

A let e = {1, 2, 3};

B console.log(e[0]);

C let f = [4, 5];

Line A — Arrays use square brackets [], not curly braces {}.

Question 5

A let colors = ["red", "blue"];

B console.log(colors[1)

C console.log(colors[1]);

Line B — The index access is missing its closing square bracket.

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