Array creation in Javascript - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the simplest way to create an empty array in JavaScript?

You can create an empty array using square brackets: []. This makes a new list that can hold items.

beginner

How do you create an array with initial values 1, 2, and 3?

Use square brackets with the values inside separated by commas: [1, 2, 3]. This creates an array holding those numbers.

intermediate

What does new Array(5) do in JavaScript?

It creates an array with 5 empty slots. The array has length 5 but no actual values set yet.

intermediate

How can you create an array from a string like 'hello'?

Use Array.from('hello'). This makes an array of each character: ['h', 'e', 'l', 'l', 'o'].

intermediate

What is the difference between [] and new Array()?

[] creates an empty array. new Array() also creates an empty array but can behave differently if you pass a number (it sets length).

Which syntax creates an array with three elements: 10, 20, and 30?

A All of the above

B [10, 20, 30]

C Array(10, 20, 30)

D new Array(10, 20, 30)

All these syntaxes create an array with elements 10, 20, and 30.

What does new Array(4) create?

A An array with 4 undefined elements

B An error

C An array with one element: 4

D An array with length 4 but empty slots

new Array(4) creates an array with length 4 but the slots are empty, not set to undefined.

How to create an array from the string 'abc'?

A Array.from('abc')

B ['abc']

C new Array('abc')

D String.toArray('abc')

Array.from('abc') creates ['a', 'b', 'c'].

Which is the correct way to create an empty array?

A []

B Both A and B

C new Array()

D Array.empty()

Both [] and new Array() create empty arrays.

What happens if you do new Array(3, 4)?

A Creates an array with length 4

B Creates an array with length 3

C Creates an array with elements 3 and 4

D Throws an error

new Array(3, 4) creates an array with two elements: 3 and 4.

Explain how to create arrays in JavaScript and the difference between using [] and new Array().

Think about how length and elements are set.

Describe how to convert a string into an array of characters in JavaScript.

Consider how strings and arrays relate.