An array is a collection of elements.
Arrays in JavaScript are not a type on their own.
Arrays are objects.
We can initialize an empty array in these 2 different ways:
const a = []
const a = Array()
The first is using the array literal syntax. The second uses the Array built-in function.
You can pre-fill the array using this syntax:
const a = [1, 2, 3]
const a = Array.of(1, 2, 3)
An array can hold any value, even value of different types:
const a = [1, 'Flavio', ['a', 'b']]
Since we can add an array into an array, we can create multi-dimensional arrays, which have very useful applications (e.g. a matrix):
const matrix = [
[1, 2, 3],
[4, 5, 6],
[7, 8, 9]
]
matrix[0][0] //1
matrix[2][0] //7
You can access any element of the array by referencing its index, which starts from zero:
a[0] //1
a[1] //2
a[2] //3
You can initialize a new array with a set of values using this syntax, which first initializes an array of 12 elements, and fills each element with the 0 number:
Array(12).fill(0)
You can get the number of elements in the array by checking its length property:
const a = [1, 2, 3]
a.length //3
Note that you can set the length of the array. If you assign a bigger number than the arrays current capacity, nothing happens. If you assign a smaller number, the array is cut at that position:
const a = [1, 2, 3]
a //[ 1, 2, 3 ]
a.length = 2
a //[ 1, 2 ]
Internally, arrays are objects. Running typeof on an array tell you object:
typeof [] //object
You can check if an object is an array by checking its constructor property:
[].constructor === Array //true
while a regular object will have
{}.constructor === Object //true