Javascript Array

Working with Arrays in Javascript

What is an Array?¶

Stores multiple elements in a single variable
No restrictions on data types
Used frequently in solving problems

How to create an Array?¶

Array with no elements
```
var arr = [];
```
Array with a few elements

var fruits = ["apple", "banana"];
var numbers = [1.2, 56, -10]
var mixed = ["apple", 1, false, null]

Nested Arrays¶

Nested arrays are arrays which contain arrays as elements

var data = [
    ["apple", "banana"],
    ["fish", "bun", 100],
];

Accessing & Modifying an Array with indexes¶

Arrays stored in a sequencial manner with an index.
Index always starts with 0

Let's see an example to access array elements with indexes

var fruits = ["apple", "banana", "grapes", "mango"];
var apple = fruits[0]
var banana = fruits[1]
var grapes = fruits[2]
var mango = fruits[3]

console.log(apple);
// output: apple

Let's see an example to update array elemets with indexes

var fruits = ["apple", "banana", "grapes", "mango"];
console.log("before update:", fruits)
// output: before update: ["apple", "banana", "grapes", "mango"]
fruits[0] = "orange"
console.log("after update:", fruits)
// output: before update: ["orange", "banana", "grapes", "mango"]

If you execute the above code you will find that we have updated the first element from value apple to orange

Accessing multi dimentional arrays with indexes¶

Multidimentional arrays are nothing but nested arrays
We don't use these multi dimentional arrays frequently

var food_items = [
    ["apple", "banana", "orange"],
    ["bun", "pizza", "cake"]
]

var apple = food_items[0][0];
var banana = food_items[0][1];
var orange = food_items[0][2];
var bun = food_items[1][0];
var pizza = food_items[1][1];
var cake = food_items[1][2];

console.log(cake)
// output: cake

Add element to an array at the end with `push()` method¶

var fruits = ["apple"]
fruits.push("banana")

console.log(fruits)
// output: ["apple", "banana"]

- Above code adds the element banana at the end of the array fruits

Add element to an array at the beginning with `unshift()` method¶

var fruits = ["apple"]
fruits.unshift("banana")

console.log(fruits)
// output: ["banana", "apple"]

- Above code adds the element banana at the beginning of the array fruits

Remove last element from an array with `pop()` method¶

var fruits = ["apple", "banana"]
var banana = fruits.pop()

console.log(fruits)
// output: ["apple"]

console.log(banana)
// output: banana

- Above code will removes the last element from array fruits and returns the element. - Returned element stored in the variable banana

Remove first element from an array with `shift()` method¶

var fruits = ["apple", "banana"]
var apple = fruits.shift()

console.log(fruits)
// output: ["banana"]
console.log(apple)
// output: apple

- Above code removes the element banana from beginning of the array fruits - Returened element stored in the variable apple

Loop over an Array¶

let fruits = ['Apple', 'Banana']
fruits.forEach(function(item, index) {
  console.log(item, index)
})

/* output:
Apple 0
Banana 1
*/

Remove items from an index position using `splice(index, numberOfElements)`¶

let vegetables = ['Cabbage', 'Turnip', 'Radish', 'Carrot']
console.log(vegetables)
// ["Cabbage", "Turnip", "Radish", "Carrot"]

let pos = 1
let n = 2

let removedItems = vegetables.splice(pos, n)
// this is how to remove items, n defines the number of items to be removed,
// starting at the index position specified by pos and progressing toward the end of array.

console.log(vegetables)
// ["Cabbage", "Carrot"] (the original array is changed)

console.log(removedItems)
// ["Turnip", "Radish"]

Copy an Array¶

let vegetables = ['Cabbage', 'Turnip', 'Radish', 'Carrot']
let shallowCopy = vegetables.slice()
console.log(shallowCopy)
// ['Cabbage', 'Turnip', 'Radish', 'Carrot']

Finding length of javascript array¶

let vegetables = ['Cabbage', 'Turnip', 'Radish', 'Carrot']
let count = vegetables.length
console.log(count)
// 4

Find the index of an item in the Array¶

let vegetables = ['Cabbage', 'Turnip', 'Radish', 'Carrot']
let pos = vegetables.indexOf('Turnip')
console.log(pos)
// 1

Reverse an array javascript¶

let vegetables = ['Cabbage', 'Turnip', 'Radish', 'Carrot']
let reverse_order = vegetables.reverse();
console.log(reverse_order)
// ["Cabbage", "Turnip", "Radish", "Carrot"]