30 Days of node

# Day 6 : Array Methods Introduction

Arrays are used to store multiple values in a single ` var `. Their index starts from ` 0 `. Today we will learn about inbuilt array methods such as push, pop, join, etc.

Create an array

Arrays can be created in any of the following ways :

```								```
// an array of names
var names = ["rj", "ricky", "alex"];
console.log(names);
//calculating the length of array
var len = names.length;
console.log(len);
//Another way to create array
var arr = new Array(3); 	// declare an array "arr" of size 3
arr = [1,5,7];  		// initialize elements of array

//OR
// declare and initialize in a single statement
var arr1 = new Array(2,5,7);
console.log("arr : " + arr);
console.log("arr 1 : " + arr1);
```
```

The Output of the code is :
```								```
>node create-array.js
[ 'rj', 'ricky', 'alex' ]
3
arr : 1,5,7
arr 1 : 2,5,7
```
```

push() Method in arrays

` push ` method in arrays is used to insert an element in the end of the array. Snippet is given below :

```								```
arr = ['a','e','i','o'];
console.log(arr);
arr.push('u');
console.log(arr);
```
```

The Output of the code is :
```								```
>node push.js
[ 'a', 'e', 'i', 'o' ]
[ 'a', 'e', 'i', 'o', 'u' ]
```
```

pop() Method in arrays

` pop ` method in arrays is used to remove the element from the end of the array. Snippet is given below :

```								```
arr = [ 5 , 5 , 8 , 7 , 6 ];
console.log(arr);
arr.pop();
console.log(arr);
```
```

The Output of the code is :
```								```
>node pop.js
[ 5, 5, 8, 7, 6 ]
[ 5, 5, 8, 7 ]
```
```

unshift() Method in arrays

` unshift ` method in arrays is used insert an element in the beginning of the array. Snippet is given below :

```								```
arr = [ 5 , 5 , 8 , 7 , 6 ];
console.log(arr);
arr.unshift(1);
console.log(arr);
```
```

The Output of the code is :
```								```
>node unshift.js
[ 5, 5, 8, 7, 6 ]
[ 1, 5, 5, 8, 7, 6 ]
```
```

shift() Method in arrays

` shift ` shift method is used to remove the element from the beginning of the array. Snippet is given below :

```								```
arr = ['b','a','e','i','o','u'];
console.log(arr);
arr.shift();
console.log(arr);
```
```

The Output of the code is :
```								```
>node shift.js
[ 'b', 'a', 'e', 'i', 'o', 'u' ]
[ 'a', 'e', 'i', 'o', 'u' ]
```
```

reverse() Method in arrays

` reverse ` method is used to reverse the order of the array such that the first element becomes the last and the last element becomes the first. Snippet is given below :

```								```
arr = ['b','e','a','o','p','n','r'];
console.log(arr);
arr.reverse();
console.log(arr);
```
```

The Output of the code is :
```								```
>node reverse.js
[ 'b', 'e', 'a', 'o', 'p', 'n', 'r' ]
[ 'r', 'n', 'p', 'o', 'a', 'e', 'b' ]
```
```

sort() Method in arrays

` sort ` method is used to sort the elements of array in term of their occurrences. Snippet is given below :

```								```
arr = ['b','e','a','o','p','n','r'];
console.log(arr);
arr.sort();
console.log(arr);
```
```

The Output of the code is :
```								```
>node sort.js
[ 'b', 'e', 'a', 'o', 'p', 'n', 'r' ]
[ 'a', 'b', 'e', 'n', 'o', 'p', 'r' ]
```
```

splice() Method in arrays

` splice ` method can be used in two ways i.e to either add the element into the array or remove the elements from the array.
Add using splice : Snippet to perform the operation of adding elements to the array using splice.

```								```
arr = ['b','e','a','o','p','n','r'];
console.log(arr);
arr.splice(2,2,'rj','nodejs');
console.log(arr);
```
```

The Output of the code is :
```								```
[ 'b', 'e', 'a', 'o', 'p', 'n', 'r' ]
[ 'b', 'e', 'rj', 'nodejs', 'p', 'n', 'r' ]
```
```

Remove using splice : Snippet to perform the operation of removing elements from the array using splice.
```								```
arr = ['b','e','a','o','p','n','r'];
console.log(arr);
arr.splice(2,2);
console.log(arr);
```
```

The Output of the code is :
```								```
>node splice-remove.js
[ 'b', 'e', 'a', 'o', 'p', 'n', 'r' ]
[ 'b', 'e', 'p', 'n', 'r' ]
```
```

concat() Method in arrays

` concat ` method is used to join two arrays and returns a new array consisting the elements of both the arrays one after other. Snippet is given below :

```								```
arr = ['tomatoes','pineapple'];
arr2 = ['mango','peach','apple'];
console.log(arr);
console.log(arr2);
var new_arr = arr.concat(arr2);
console.log(new_arr);
```
```

The Output of the code is :
```								```
>node concat.js
[ 'tomatoes', 'pineapple' ]
[ 'mango', 'peach', 'apple' ]
[ 'tomatoes', 'pineapple', 'mango', 'peach', 'apple' ]
```
```

indexOf() Method in arrays

` indexOf ` method is used to return the first index of the element passed within the array or otherwise it will return ` -1 ` if the value is not found. Snippet is given below :

```								```
arr = [ 5 , 2 , 8 , 5 , 6 ];
console.log(arr);
var pos = arr.indexOf(8);
console.log("index of 8 is : " + pos);
var pos1 = arr.indexOf(5);
console.log("index of 5 is : " + pos1);
```
```

The Output of the code is :
```								```
>node indexOf.js
[ 5, 2, 8, 5, 6 ]
index of 8 is : 2
index of 5 is : 0
```
```

lastIndexOf() Method in arrays

` lastIndexOf ` method is used to return the last index of the element passed within the array or otherwise it will return ` -1 ` if the value is not found. Snippet is given below :

```								```
arr = [ 5 , 2 , 8 , 5 , 6 ];
console.log(arr);
var pos = arr.lastIndexOf(5);
console.log("index of 5 is : " + pos);
```
```

The Output of the code is :
```								```
>node lastIndexOf.js
[ 5, 2, 8, 5, 6 ]
index of 5 is : 3
```
```

join() Method in arrays

` join ` method is used to join the elements into a string and returns the string. The elements will be separated by a specific separator while joining which will be passed while calling the method. The default separator is ` , (comma) ` . Snippet is given below :

```								```
arr = [ 5 , 2 , 8 , 5 , 6 ];
arr1 = ['a','b','c','d'];
console.log(arr);
console.log(arr1);
var str = arr.join();
var str1 = arr1.join(":");
console.log(str);
console.log(str1);
```
```

The Output of the code is :
```								```
>node join.js
[ 5, 2, 8, 5, 6 ]
[ 'a', 'b', 'c', 'd' ]
5,2,8,5,6
a:b:c:d
```
```

slice() Method in arrays

` slice ` method is used to extract a section of an array and returns a new array. Slice method take two arguments i.e start and end. If both elements are omitted then it will slice the whole array. Syntax is : ` slice(start,end) `

1. start : This is an integer which specifies where to start. The default value is index ` 0 `. If omitted like this :: ` slice(,end) ` it will use the default value as start. We can also start from the end by using negative values . This is optional.
2. end : This is an integer value which specifies where to end (last index excluded). If omitted like this :: ` slice(start,) ` it will slice upto the last element. We can use negative values to select from the end. This is optional.
Note : It will not change the original array.
```								```
arr = [ 5 , 2 , 8 , 5 , 6 ];
arr1 = ['a','b','c','d'];
console.log(arr);
console.log(arr1);
var str = arr.slice(2,4);
var str1 = arr1.slice(-2,-1);
console.log(str);
console.log(str1);
```
```

The Output of the code is :
```								```
>node slice.js
[ 5, 2, 8, 5, 6 ]
[ 'a', 'b', 'c', 'd' ]
[ 8, 5 ]
[ 'c' ]
```
```

every() Method in arrays

` every ` method is used to check whether a condition in fulfilled by all the elements or not. ` every ` method returns ` true ` if the condition is satisfied by all the elements of the array otherwise ` every ` method will return ` false ` . Snippet is given below :

```								```
arr = [2,4,6,8,10];
arr1 = [2,3,4,6,8];
function even(value){
if( (value % 2) == 0){
return true;
}else{
return false;
}
}

var out = arr.every(even);
var out1 = arr1.every(even);
console.log("Output of array 1 : " + out);
console.log("Output of array 2 :" + out1);
```
```

The Output of the code is :
```								```
>node every.js
Output of array 1 : true
Output of array 2 :false
```
```

filter() Method in arrays

` filter ` method is used to create a new array , filled with all the elements that passes a test condition usually passed as a function , from the current array . Snippet is given below :

```								```
arr = [2,4,6,8,10];
arr1 = [2,3,4,6,8];
function even(value){
if( (value % 2) == 0){
return true;
}else{
return false;
}
}

var out = arr.filter(even);
var out1 = arr1.filter(even);
console.log("Output of array 1 : " + out);
console.log("Output of array 2 :" + out1);
```
```

The Output of the code is :
```								```
>node filter.js
Output of array 1 : 2,4,6,8,10
Output of array 2 : 2,4,6,8
```
```

find() Method in arrays

` find ` method returns the first value in the array which passes a test provided as a function. If no element matches the condition , it will return ` undefined `. Snippet is given below :

```								```
arr = [2,4,6,8,10];
arr1 = [2,3,4,7,8];
function odd(value){
if( (value % 2) == 1){
return true;
}else{
return false;
}
}

var out = arr.filter(odd);
var out1 = arr1.filter(odd);
console.log("Output of array 1 : " + out);
console.log("Output of array 2 :" + out1);
```
```

The Output of the code is :
```								```
>node find.js
Output of array 1 :
Output of array 2 :3,7
```
```

forEach() Method in arrays

` forEach ` method in arrays is a loop which is used to call a function for each element in the array. Snippet is given below :

```								```
var arr = ['1', '2', '3','5','8'];

arr.forEach(function(element) {
console.log(element);
});
```
```

The Output of the code is :
```								```
>node forEach.js
1
2
3
5
8
```
```

reduce() Method in arrays

` reduce ` method is used to reduce the array to a single value. This method executes the provided function for each value of the array and stores the result in accumulator. Note : It does not execute on array with no values. Snippet is given below :

```								```
arr = [ 5 , 5 , 8 , 7 , 6 ];
console.log(arr);
function mul(value ,total){
total = value * total;
}
var output = arr.reduce(mul);
console.log("The product of the array is : " + output);
```
```

The Output of the code is :
```								```
>node reduce.js
[ 5, 5, 8, 7, 6 ]
The product of the array is : 8400
```
```

Summary

In this article we learned about arrays , how we can create arrays in node.js and array methods such as push , pop , shift , unshift , reverse , sort , splice , concat , indexOf , lastIndexOf , join , slice , every , filter , find , forEach , reduce , etc. All this methods are explained with code examples .

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