Arrays in JS
Declaration
const a = []
const a = Array()
pre-fill the array
const a = [1, 2, 3]
const a = Array.of(1, 2, 3)
An array can hold any value, even values of different types:
const a = [1, 'Flavio', ['a', 'b']]
`const matrix = [
[1, 2, 3],
[4, 5, 6],
[7, 8, 9]
]
matrix[0][0] //1
matrix[2][0] //7`
Declare and define arrays at same time
Array(12).fill(0)
Length of array
const a = [1, 2, 3]
a.length //3
How to add an item to an array
At the end
a.push(3);
at the beginning of an array
a.unshift(5);
How to remove elements from the array
remove an item from the end of an array using the pop() method:
a.pop()
remove an item from the beginning of an array using the shift() method:
a.shift()
How to join two or more arrays
You can join multiple arrays by using concat():
const a = [1, 2]
const b = [3, 4]
const c = a.concat(b) //[1,2,3,4]
spread operator (...) in this way:
const a = [1, 2]
const b = [3, 4]
const c = [...a, ...b]
c //[1,2,3,4]
How to find a specific item in the array
You can use the find() method of an array:
a.find((element, index, array) => {
//return true or false
})
A commonly used syntax is:
a.find(x => x.id === my_id)
a.findIndex((element, index, array) => {
//return true or false
})
Another method is includes():
a.includes(value)
Returns true if a contains value.
a.includes(value, i)
Returns true if a contains value after the position i.
Thanks for reading <3
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