30 Days of node

Day 6 : Array Methods

30 Days of Node | Node.js Tutorial series



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 :
								
>node splice-add.js
[ '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;
    return 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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