# Arrays in Javascript

# Arrays

In JavaScript, an array is a special variable that can store different data types and also allows to store duplicates elements. Each value is called an element specified by an index.

## Creating JavaScript Arrays

There are three ways to create an array.

 **1. Using array constructor**

```JavaScript
let num= new Array()
``` 
The `num` array is empty which does not hold any elements.

- If we know the number of elements that the array will hold , then we create the array with initial size.

```Javascript
let names=Array(19)
``` 
- If we want to create an array and initialise with some elements, then create as follows:

```JavaScript
let country=new Array("India","USA", "Russia");
``` 
 **2. Using square brackets[ ] (or, Array Literal Notation)**

This is the most preferred way to create an array. We use square brackets ([ ]) to wrap a comma separated list of elements.

```JavaScript
let arr=[1,2,3,4]
``` 
**3. Using split**

We can split a string at different positions and then change to an array. Lets see the examples below:

```javascript
let course='JavaScript'
const courseArr=course.split('')
console.log(courseArr) //["J","a","v","a","S","c","r","i","p","t"]
``` 
## Accessing JavaScript array elements using index

An array index starts from 0. To access an element in an array, we specify an index in the square brackets [ ].

```javascript
let companies=['Amazon', 'Google', 'Netflix']
console.log(companies[2]) // 'Netflix'
``` 

## Modifying array element

An array is mutable(modifiable).  We can change the value of an element in an array. Lets see the code example below:

```javascript
let nums=[1,2,3,4,5]
nums[0]=10
nuts[3]=20
console.log(nuts) // [10,2,20,4,5]
``` 
## Methods to manipulate array

**1. length()**
- To know the size of an array

```javascript
let numbers=[1,2,3,4,5]
console.log(numbers.lenght) // 5
``` 
**2. indexOf()**
- To check if an element exist in an array. If it exists, it returns the index of the element else return -1.

```JavaScript
let arr=['Amazon', 'Netflix', 'Uber']
console.log(arr.indexOf('Uber'))   //2
``` 
**3. lastIndexOf()**
- It returns the index of the last element in the array, if it exist else returns -1.

```
let companies=['Amazon', 'Netflix', 'Uber','Apple']
console.log(companies.lastIndexOf('Uber'))   //2
console.log(companies.lastIndexOf('Infosys'))   //-1
``` 
**4. Array.isArray()**
- To check if the given data is an array or not. It returns boolean(true or false).

```
let companies=['Amazon', 'Netflix', 'Uber','Apple']
console.log(Array.isArray(companies)) //true

let number=8
console.log(Array.isArray(number)) //false
``` 
**5. toString()**
- It converts array to string

```
let companies=['Amazon', 'Netflix', 'Uber','Apple']
console.log(companies.toString()) // Amazon,Netflix,Uber,Apple
``` 
**6. concat()**
- It concatenates two arrays.

```
let companies=['Amazon', 'Netflix', 'Uber','Apple']
let location=['USA', 'India','UK']
let companiesLocation=companies.concat(location)
console.log(companiesLocation) //['Amazon', 'Netflix', 'Uber','Apple','USA', 'India','UK']
``` 
**7. join()**
- It is used to join the elements of the array, the argument we passed in the join method will be joined in the array and return as a string. By default, it joins with a comma, but we can pass different string parameter which can be joined between the items.

```
let companies=['Amazon', 'Netflix', 'Uber','Apple']
console.log(companies.join()) //Amazon,Netflix,Uber,Apple
console.log(companies.join('')) //AmazonNetflixUberApple
console.log(companies.join(' ')) //Amazon Netflix Uber Apple
console.log(companies.join('#')) //Amazon # Netflix # Uber # Apple
console.log(companies.join(,)) //Amazon,Netflix,Uber,Apple
``` 
**8. fill()**
- It fills the array elements with a static value.

```
let values=Array(5).fill('Y') //[Y,Y,Y,Y,Y] 
``` 
**9. push()**
- To add an element to the end of an existing array.

```
let companies=['Amazon', 'Netflix', 'Uber','Apple']
companies.push('Meta')
console.log(companies) // ['Amazon', 'Netflix', 'Uber','Apple','Meta']
``` 
**10. pop()**
- To remove an element from the end of the existing array.

```
let companies=['Amazon', 'Netflix', 'Uber','Apple']
companies.pop() // remove an element from the end
console.log(companies) // ['Amazon', 'Netflix', 'Uber']
``` 
**11. unshift()**
- To add an element to the beginning of an existing array.


```
let companies=['Amazon', 'Netflix', 'Uber','Apple']
companies.unshift('Meta')
console.log(companies) // ['Meta','Amazon', 'Netflix', 'Uber','Apple']
``` 
**12. shift()**
- To remove an element from the beginning of an existing array.

```
let companies=['Amazon', 'Netflix', 'Uber','Apple']
companies.shift() // remove an element from the beginning
console.log(companies) // ['Netflix', 'Uber','Apple']
``` 
**13. reverse()**
- It reverse the order of an array.

```
let numbers=[1,2,3,4,5]
numbers.reverse() 
console.log(numbers) //[5,4,3,2,1]
``` 
**14. sort()**
- It arrange array elements in ascending order.

```
let companies=['Amazon', 'Netflix', 'Uber','Apple']
companies.sort()
console.log(companies) //['Amazon','Apple','Netflix','Uber']
``` 
**15. slice()**
- It returns a new array containing a portion of the array. It takes two parameters: `starting and ending position`. It doesn't include the ending position.


```
let companies=['Amazon', 'Netflix', 'Uber','Apple','Meta','Ola']
companies.slice(1,3) //['Amazon','Apple','Meta','Ola']
``` 

**16. splice()**
- It takes three parameters: `starting position, number of times to be removed and elements to be added`.

```
let numbers = [1, 2, 3, 4, 5, 6]
numbers.splice(3, 3, 7, 8, 9)
  console.log(numbers.splice(3, 3, 7, 8, 9))  // -> [1, 2, 3, 7, 8, 9] //it removes three elements and replace with three elements.
```