Array index

JavaScriptJunior~1 min read

An array index is the position number of an element in the array. It lets you access, change, or remove the element you need.

Key facts

Indexing starts at zero (0). The first element has index 0, the second 1, the third 2, and so on.
An index is simply a numeric key of an array element.
An element is accessed through square brackets: array[index].

Example:

javascript

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

console.log(fruits[0]); // "apple", the first element
console.log(fruits[1]); // "banana", the second element
console.log(fruits[2]); // "cherry", the third element

Changing an element by index:

javascript

fruits[1] = "orange";
console.log(fruits); // ["apple", "orange", "cherry"]

Array length and the last index

The .length property shows the number of elements.
The index of the last element always equals length - 1.

javascript

const numbers = [10, 20, 30, 40];
console.log(numbers.length); // 4
console.log(numbers[numbers.length - 1]); // 40

What if you access a nonexistent index?

javascript

console.log(fruits[10]); // undefined

In short:

Concept	Description
Index	position of an element in the array
First element	index `0`
Last element	index `length - 1`
Nonexistent index	returns `undefined`

Short Answer

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Array index

#Key facts

#Example:

#Changing an element by index:

#Array length and the last index

#What if you access a nonexistent index?

#In short:

Short Answer

Key facts

Example:

Changing an element by index:

Array length and the last index

What if you access a nonexistent index?

In short: