Arrays

Array data is ordered by indexes. Arrays are actually objects, having indexes (numbers from 0 to length -1) as keys.

let fruits = ['apples', 'pears', 'oranges'];

fruits[1]
→ "pears"

Arrays: Access, Add, Remove, and Update Elements

▸ let fruits = ['Apple']

▸ fruits.push('Pear')      // Add to the end of the array
2                           // The new length of the array

['Apple', 'Pear']

▸ fruits.unshift('Orange') // Add to the start of the array
3                           // New length of the array

['Orange', 'Apple', 'Pear']

▸ fruits[1]                 // Access second element of the array
'Apple'

▸ fruits.length             // How many items are in the array?
3

▸ fruits[1] = 'Lemon'       // Changes item in index 1 to "Lemon"
"Lemon"

['Orange', 'Lemon', 'Pear']

▸ fruits.splice(1, 0, 'Grapes') // Insert at index 1 a new element
[] // < Splice is supposed to delete things (see below)
   //   In this case we're deleting 0 elements and inserting one.

['Orange', 'Grapes', 'Lemon', 'Pear']

▸ fruits.indexOf('Lemon')    // Get the index of 'Lemon'
2

▸ fruits.splice(2, 1)        // Delete 1 item from index 2
["Lemon"]

['Orange', 'Grapes', 'Pear']

▸ fruits.pop()               // Remove the last item
"Pear"

['Orange', 'Grapes']

▸ fruits.shift()             // Remove the first item
"Orange"

['Grapes']

Iterating over Arrays

var arr = [42, 7, -1]

// Using for-loop
for (var index = 0; index < arr.length; ++index) {
    // Do something
}

// Using forEach
arr.forEach((current, index, inputArray) => {
    // Do something
})

// Using for...of
for (let current of arr) {
    // Do something
}