Array creation in JavaScript -oracleappshelp.com

The blog describes the Array creation in JavaScript. An array is a group of element values. The JavaScript supports array creation in 3 ways

By using Array Literals
By creating Array Instance
By creating Array Constructor

JavaScript Array creation using Literals

The JavaScript allows to create array using literals. The array is defined with [ ] with the list of values. The below given is the example of array using literals

let student = ["Mohit", "Rohit", "Nitin"];
alert( student[0] ); // returns Mohit
alert( student[1] ); // returns Rohit
alert( student[2] ); // returns Nitin

Array allow to replace the element value at nth position

student[2] = 'John';

Array allows to add new element to an existing array object

student[3] = 'Robert';

Array length can be determined

alert( student.length ); // 3

An array can support mix of values

// mix of values
let student = [ '30', { name: 'Mohit Sharma' }, true, function() { alert('stuent is enrolled for the course'); } ];

// get object at index 1 
alert( student[1].name ); // Mohit Sharma

// get the function at index 3 
student[3](); // prints stuent is enrolled for the course

Empty array creation in JavaScript

JavaScript allows supports empty array as given below

let student = new Array();  // empty array using new Array()
let student = [];           // empty array using literals

Array creation using new keyword

The JavaScript allows to create object using new keyword

var student =new Array();

<script>  
var count;  
var student = new Array();  
student[0] = "Mohit";  
student[1] = "Rohit";  
student[2] = "Vivek";  
  
for (count=0;count<student.length;count++){  
document.write(student[count] + "<br>");  
}  
</script>

Array creation using constructor

The JavaScript allows to create object using constructor

<script>  
var count;  
var student = new Array("Mohit", "Rohit", "Vivek");  
for (count=0;count<student.length;count++){  
document.write(student[count] + "<br>");  
}  
</script>

Methods	Description
concat()	method allows to concatenate two or more arrays Syntax: array.concat(array1,array2,….,arrayn) Return: Combined values of all arrays
copywithin()	method copies the part of the array elements and returns the modified array Syntax: array.copyWithin(target, start, end) Return: the modified array elements
entries	method allows to iterate over each key/value pair in an array Syntax: array.entries() Return: the newly created array iterator object
every()	method validates if all the array elements are satisfying the provided function conditions. Syntax: array.every(callback(currentvalue,index,arr),thisArg) Return: Boolean value
flat()	The method concatenates all the elements of the given multidimensional array and flattens it into 1 dimensional array recursively till the specified depth. Syntax: arr.flat(<depth>); Return: new array containing all the sub-array elements of the multi dimensional array
flatMap()	method maps array elements via mapping function and results into a new array. Syntax: arr.flatMap(function callback(currentValue[ , index[ , array]]) Return: new array where each element is the result of the callback function
fill()	method fills array elements with static values Syntax: arr.fill(value[, start[, end]]) Return: the modified array
from()	method creates a new array with copied element of another array Syntax: Array.from(object,map_fun,thisArg); Return: return new array object
filter()	method returns the new array containing the elements that pass the provided function conditions. Syntax: array.filter(callback(currentvalue,index,arr),thisArg) Return: New array with filtered array elements
find()	method returns the value of the first array element that satisfies the specified condition
findIndex()	method returns the index value of the first element that satisfies the specified condition
forEach()	method invokes the provided function once for each element of an array
includes()	method validates if given array contains the specified element
indexOf()	method searches the specified array element returns the index of the first match
isArray()	method validates if the passed value is an array
join()	method joins the array elements as a string
keys()	method creates an iterator object that contains loops through the given array keys
lastIndexOf()	method searches the specified element in the given array and returns the index of the last match
map()	method calls the specified function for every array element and returns the new array
of()	method creates a new array from a variable number of arguments, holding any type of argument
pop()	method removes and returns the last array element
push()	method adds one or more elements to the end of an array
reverse()	method reverses the array elements
reduce(function,initial)	array executes a provided function for each value from left to right and reduces the array to a single value
reduceRight()	array executes a provided function for each value from right to left and reduces the array to a single value
some()	method validates if any array element passes the test of the implemented function
shift()	method removes and returns the first element of an array
slice()	method returns a new array containing the copy of the part of the given array
sort()	method returns the element of the given array in a sorted order
splice()	method add/remove elements to/from the given array
toLocaleString()	method returns a string containing all the elements of a specified array
toString()	method converts the elements of a specified array into string form, without affecting the original array
unShift()	method adds one or more elements in the beginning of an array
values()	method creates a new iterator object carrying values for each index in the array

JavaScript Array flat() example

// Array flat() example	
<script>
var teachers=['Angela','Cameron',['Stephnie','Brida']];
var newTeachersArr=teachers.flat(); //using array flat() method  
//create a new array with one dimesnioanl array
document.write("usgae of array flat() :  "+newTeachersArr);
</script>

JavaScript Array entries() example

  <script>  
	var subjects =['English','Math','Science','French'];  
    var itr=subjects.entries();  
    for(var i of itr) 
    {  
        document.write(i+"</br>");  
    }  
  </script>

JavaScript Array fill() example

<script>  
var subjects =['English','Math','Science','French'];  
var result=subjects.fill("Computer Science");  
document.writeln(arr);  
</script>

JavaScript Array from() example

<script>  
var strText=Array.from("Converts String to Array of Alphabet"); //The string will get converted to an array.  
document.write("Array contains: <br>" +strText);  
 </script>

JavaScript Array concat(), entries() example

<script>  
// Array example for concat() 
var student1 = ["Mohit", "Rohit", "Vivek"];  
var student2 = ["John", "Smith", "Robert"]; 
var totalStudents=student1.concat(student2);  
document.writeln(totalStudents); 

var itr=totalStudents.entries();  
    document.write("usgae of array entries() :"+"<br>");  
      for(var e of itr) //for loop using var.  
    {  
        document.write(e+"</br>");  
    }  }  
</script>