# JavaScript Array Methods

## **javascript array**

basically, an array is a collection of values. It is a list of items, that contains a list of elements which store multiple values under a single variable. where each item has a particular position in the list.JavaScript array can store mixed data formats in a single array.

## **Declaring an array**

In general, there are two ways to declare an array. The syntax is as follows:

```javascript
let array1 = [1, 4, 8, 20, 16, ...]; //  way 1
let array2 = new Array( 1, 2, 3, 4, 5); // way 2
```

## **Array methods**

### push():

To add a new one or more element at the end of an array, we can use the push() method. This method will modify your existing array.

```javascript
let arr = [1, 6, 9, true,];
arr.push(100);
console.log(arr);
 // output- [ 1, 6, 9, true, 100 ]
```

### [pop()](https://www.geeksforgeeks.org/javascript-array-pop-method/):

This method removes the last element present in the array and returns that element. This method changes the length of the array.

```javascript
let arr = [1, 6, 9, true, 100];
arr.pop();
console.log(arr);
// output- [ 1, 6, 9, true ]
```

### unshift()

It is similar to how the push() method works, the **unshift()** method takes your array and adds one or more elements to the start of the array instead of the end. This method will also modify your existing array.

```javascript
let arr = [1, 6, 9, true,];
arr.unshift(100);
console.log(arr);
// output-[ 100, 1, 6, 9, true ]
```

### [shift()](https://www.geeksforgeeks.org/javascript-array-pop-method/):

This method removes the first element present in the array and returns that element. This method changes the length of the array.

```javascript
let arr = [1, 6, 9, true, 100];
arr.shift();
console.log(arr);
// output-[ 6, 9, true, 100 ]
```

### concat():

By using this method can merge two or more arrays into a new array. It does not modify the existing arrays but creates a new one.

```javascript
let arr1 = [1, 2, 3, 4];
let arr2 = [4, 5, 6, 7];

console.log(arr1.concat(arr2));
 // output [ 1, 2, 3, 4, 4, 5, 6, 7]
```

### indexof():

This method is used to find the index of a particular element in an array. It aslo returns the numerical index or -1 if the element is not present in the array.

```javascript
let arr = [1, 6, 9, true,];
console.log(arr.indexOf(1));
console.log(arr.indexOf(2));
//output-
//0
//-1
```

### lastIndexOf():

The method returns the last index at which a given element can be found in the array, or -1 if it is not present.

```javascript
let arr = [1, 6, 9, true, 1];
console.log(arr.astIndexOf(1));
//output- 4
```

### includes():

This method is used to check whether the array contains the specified element or not. Depending upon whether that element is present or not, it will return **true** or **false** respectively.

```javascript
let arr = [1, 6, 9, true, 100];
console.log(arr.includes(1));
console.log(arr.includes(2));
//output-
// true
// false
```

### fill():

This method fills specified elements in an array with a value and overwrites the original array. The start and end position can be specified. If not, all elements will be filled.

**syntax -** `array.fill{value, start(default 0), end(default array.length)}`

```javascript
let arr = [1, 6, 9, true, 100];
console.log(arr.fill(0, 2, 4));

// output -[ 1, 6, 0, 0, 100 ]
```

### slice():

This method extracts the part of the given array and returns it. This method doesn't change the original array.

***syntax-*** `array.slice(start,end)`

```javascript
let arr = [1, 6, 9, true, 100];
console.log(arr.slice(1, 4));
//output-[ 6, 9, true ]
```

### splice():

This method is used to add/remove the elements to/from the existing array. By specifying the index and number of elements to delete, it modifies the array.

***syntax-*** `array.splice(index, delete, item1, ....., itemX)`

***index-The position to add/remove items.  
Negative value defines the position from the end of the array.***

***delete- The number of elements to be removed.***

***items- The elements to be inserted.***

```javascript
let arr = [1, 6, 9, true, 100, 23];
arr.splice(1, 2, 11, 22);
console.log(arr);
//output-[ 1, 11, 22, true, 100, 23 ]
```

### **reverse():**

This method is used to reverse the order of elements in the array. It does not reverse the contents of the array but just the order itself.

```javascript
let arr = [1, 6, 9, 328, 100];
console.log(arr.reverse());
//output-[ 100, 328, 9, 6, 1 ]
```

### map():

This array method calls the specified function for every array element and returns the new array. This method doesn't change the original array.

```javascript
let maths = [1, 4, 9, 16, 25];
console.log(maths.map(Math.sqrt));
//output-[ 1, 2, 3, 4, 5 ]
```