Accessing array elements in Javascript - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is an array in JavaScript?

An array is a list that holds multiple values in order. You can think of it like a row of boxes, each with a number to find what’s inside.

beginner

How do you access the first element of an array named fruits?

Use fruits[0]. Arrays start counting at 0, so the first box is number 0.

beginner

What happens if you try to access an index that is outside the array length?

You get undefined because there is no value stored at that position.

intermediate

How can you find the last element of an array arr without knowing its length?

Use arr[arr.length - 1]. arr.length gives the number of items, so subtract 1 to get the last index.

intermediate

What is the difference between arr[1] and arr['1'] in JavaScript?

There is no difference. JavaScript converts the string '1' to the number 1 when accessing array elements.

What index do arrays in JavaScript start counting from?

A 1

B Depends on the array

C -1

D 0

Arrays always start at index 0, so the first element is at position 0.

What will arr[5] return if arr has 3 elements?

A undefined

B The 6th element

C Error

D null

Accessing an index outside the array length returns undefined, not an error.

How do you get the last element of an array myArray?

A myArray[myArray.length - 1]

B myArray[-1]

C myArray[myArray.length]

D myArray.last()

The last element is at index length minus 1 because counting starts at 0.

What does arr['2'] access in JavaScript?

A The element at index '2' as a string key

B An error because index must be a number

C The element at index 2

D The whole array

JavaScript converts string '2' to number 2 when accessing array elements.

If colors = ['red', 'green', 'blue'], what is colors[1]?

A 'red'

B 'green'

C 'blue'

D undefined

Index 1 is the second element, which is 'green'.

Explain how to access elements in a JavaScript array and what happens if you use an index outside the array.

Think about how you find items in a list by their position.

Describe how to get the last element of an array without knowing its length beforehand.

Remember the array length counts items, but indexes start at zero.