Explain how to Create Arrays in Java Script

An array is an ordered set of data elements which can be accessed through a single variable name.

An array is made up of a set of slots, it is with each slot assigned to a single data element in the array. We can access the data elements either sequentially (or) by their index.

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2
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                                    Structure of array.

® In java script an ‘array’ is  a special type of object.

® An array is a data store.

Creating array:- Java script arrays can be constructed n three different ways.

1) var arr = [“ sun “, “Mon”, “Tue”];

® This creates an array of ‘3’ elements each holding a text string.

®Notice that the array of elements are surrounded by “square” brackets”. the second approach is to create an array object using the keyword “new” and set by set of elements to store.

2) var are = new Array (“sun”, “Mon”, “Tue”);

3) Using this construct the contents of an array are surrounded by parenthesis because they are parameters to the constructor of the array object.

Finally an empty array object which has space for no.of elements can be created.

3) var arr = new Array (5);

Java script arrays can hold mixed data types as follows:-

4) var arr = new Array (“Surya”, 24, 3.14);

Adding elements to an array:- Array elements are accessed by their index. The index denotes the position of the element in an array a in “for” loops they are start from “Zero”.

Eg:- 1) arr [4] = “sun”;           2) arr [10] = 20;

Accessing array numbers:- The elements in the array are accessed through their index values. The same access method is used to find elements and to change their values.

If you want to know how many elements have been stored in an array the ‘length’ attribute is used. The index no’s run from ‘o’ to ‘length-1’.

Eg:- var len = arr. length;

Object based array functions:- in java script an array can act like an object.

concat (array 2.[array 3.[array n]]]:-  A list of arrays are concatenated on to the end of the array and a new array returned.

 var first = [“Mon”, “Tue”, 28, 3.14];

 var second = [“One”, “Tue”, 4];

 var result = first.concat (second);

Join (string):- Some times all of the elements in an array joined together as a string. it parses through the array creating a string of all elements”.In the resulting string the elements are separated using the optional string parameters (i.e., “, “).

Eg:- first.join [“,”];

pop:- This function removes the last element from the array and reduces the no.of elements in the array by one.

Eg:- first.pop( );

push:- Adds a list of elements to the end of the array. The elements are separated using “,” in the parameter list.

Eg:- first.push (“ One”, “Two”, 89.14);

reverse:- As the name suggest this function swaps all of the elements in the array.

Eg:- first.reverse ( );

Shift( ): Removes the first elements of the array and shortens its length by one.

Syntax:- Shift( );

sort( ):- The array is sorted into lexicographic dictionary order. Elements in the array which are not text are first converted to strings. Then the sort operation is performed.

Slice(start, [finish]): Sometimes you need to extract a range of elements from an array. The ‘Slice’ function is used to do this.

Two parameters are possible. The first element which you want to remove is specified in the just parameter. The last element you want is specified in the second one.

If you only give  a single parameter all elements from the specified one to the end of the array are. Selected.

Once the elements have been sliced they are returned as a new array.The original array is unaltered by this function.

Program:

<html>
<head>
<title> array operations </title>
</head>
<body>
<script language = “ java script”>
document.write(“<h1> array functions </h1>”);
var first = ‘[“Mon,”, “June”, 34, 76.34, “Wed”];
document.write (“ <p>);
document.write (first. Join (“,”));
document.write (“<br>”);
first. Pop ( );
document.write (first. Join (“,”));
document.write (“<br>”);
first. Push (“one”, “two”, “three”, 76.9);
document.write (first join (“ ,”));
document.write(“ <br> “);
first. shift ( );
first.shift ( );
document.write (first.join (“, “));
document.write(“<br>”);
first. shift ( );
first. shift ( );
document.write(first. Join (“,”));
document.write (“</p>”);
document. close ( );
</script> 
</body> 
</html>

o/p:-

Array functions
Monday, Tuesday, 34, 76.34, Wednesday
Monday, Tuesday, 34, 7.34.
Monday, Tuesday, 34.64,34,, one, two, three, 76.9.
7.69, Three, two, one, 76.4, 34, Tuesday, Monday.
Two, One, 76.34,34, Tuesday, Monday.

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