JavaScript Array

Array -

An array in JavaScript is an object data type, it can store similler annd different kind data types.

For example - it can store string, numbers, object and even other arrays, And also we can store mix of it.

const element = ["Car", "Bus", "Bike", 1, 45, 76 [2,4,6,8]];

An array contains more than one value with a numerical index, where the index starts from 0. Thus it holds its value in a key-value pair.

There are 2 ways to construct array in JavaScript -

1. By array literal

2. By using new keword -

   • Instance of Array (using new keyword)
   • Array constructor (using new keyword)

1. JavaScript array literal-

A collection of elements wrapped between the pair of square brackets [ ] represent an array literal in JavaScript. The size of this array literal is specified by the element inside the brackets, and values are separated by comma ( , ).

The syntax of creating array using array literal is given below:

var arrayName = [value2, value2, value3, ....., valueN];

Let's see the simple example of creating and using array in JavaScript.

var arr = ["Sam", "Jerry", "Rock"];  
for (i = 0; i < arr.length; i++){  
console.log(arr[i]);
}

2. Creating array using 'new' keyword -

New keyword in JavaScript is used to create an instance of an object that has a constructor function. On calling the constructor function with ‘new’ operator, the following actions are taken:

• A new empty object is created.
• The new object’s internal ‘Prototype’ property (proto) is set the same as the prototype of the constructing function.
• The ‘this’ variable is made to point to the newly created object. It binds the property which is declared with ‘this’ keyword to the new object.
• A newly created object is returned when the constructor function returns a non-primitive value (custom JavaScript object). If the constructor function returns a primitive value, it will be ignored. At the end of the function, ‘this’ is returned if there is no return statement in the function body.

The syntax of creating array directly using new-

var arrayName = new Array ();

• Creating instance of array using new keywor -

var i;  
var emp = new Array ();  
emp [0] = "Harry";  
emp [1] = "Duke";  
emp [2] = "Jackson";  

for ( i = 0; i < emp.length; i++){    
console.log(emp[i]);
}

• Creating array constructor using new keywor -

  var emp = new Array("Rohan","Henrry","Smith");  
  for ( i = 0; i < emp.length; i++){  
  console.log(emp[i]); 
  }
  

Basic operations on arrays

• Adding an element to the end of an array-

let seaName = ['Black Sea', 'Caribbean Sea', 'North Sea', 'Baltic Sea'];
seaName.push('Red Sea');

console.log(seaName);

Output -

[ 'Black Sea', 'Caribbean Sea', 'North Sea', 'Baltic Sea', 'Red Sea' ]

• Adding an element to the beginning of an array-

let seaName = ['Black Sea', 'Caribbean Sea', 'North Sea', 'Baltic Sea'];
seaName.unshift('Red Sea');

console.log(seaName);

Output -

[ 'Red Sea', 'Black Sea', 'Caribbean Sea', 'North Sea', 'Baltic Sea' ]

• Removing an element from the end of an array-

  let seaName = ['Black Sea', 'Caribbean Sea', 'North Sea', 'Baltic Sea'];
  const lastElement = seaName.pop();
  console.log(lastElement);
  

  Output -

  Baltic Sea
  

• Finding an index of an element in the array-

let country = ['India', 'Japan', 'South Korea', 'USA'];
let index = country.indexOf('USA');

console.log(index); //4

Some Methods used in array operation are below -