FrontEnd/javascript.txt at main · shortnotes/FrontEnd · GitHub

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javacscript:
--------------------
javascript is a scrpting program for useful to develop front end applications,

But recently they were developed node.js so from node.js application javscript
useful as backend application also.

javacsript is implemented in many other application
angular, typescript, reactjs, nodejs, jquery
MOngoDB

javascriptscript is one of concept is developed by brendon eiche 1995.
live script.


java it is Object Oriented Programm and it supports OOPS,
class, object, polymorphism,


javascrit is script based program  language or Object based language
. 2015 javascript also introduced some
of the features like

class
object
const
let
array
arrowfunction or lamda expression
var


javascript is implements some features in the year 2015 .

ECMA 2015
(European Computer Manufacturer Association)

ECMA 2015 standard or ES6 standards: Any


javascript is a light weight program,


javascript:
--javscript support operators
--javscripts data typescript
--javascript supports array , Object
--javascript is also control statement
--string
--event handling Mechanism
---validate form


Data types:
------------------------
number
boolean
null
string


javascript also embedded in html
synatx:

<script type="text/javascript">
-----
</script>

OR

<script language="javascript">
----
</script>


Basic Example program to inclue javascript code in Body section HTML:
--------------------------------------------------------------

<html>
<head>
</head>
<body>
<script type="text/javascript">
document.write("Hello world");
</script>
</body>
</html>


Example program to include Javscript code in Head Section:
-------------------------------------------------------------------
<html>
<head>
<script type="text/javascript">
document.write("Hello world");
</script>
</head>
<body>
</body>
</html>


Operators:
-----------------------------
Operator is a symbol performs action between the operands.


1. Arithmetic
+   5+2=7
-
*
/
%


2. Assignement Operator:
=
var a=10;
+=
-+
*=
/=
%=
4
3. String Operators:
----------------------
+
var str1="sravan";
var str2="reddy";
var str3=str1+str2;
    str3="sravanreddy"

	In this example + is an concatenation


4. comparission Operators:OR Relational Operators
----------------------------------
<
>
<=
>=
!=
==

5. Logical Operator:
------------------
&&
||
!


Control Statements in Javscript:
--------------------------------
control statements in java is useful for controlling the flow of execution

conditional
Iterative Or Loop statement


conditional statatements:
if
if-else
elseif
nestedif
switch


loop statement:
for
while
do-while


function in javascript:
----------------------------
Definition: a function is a statements or a group of statement executed by a single unit.
In javascript function definition defined in following ways

syntax:

function function name()
{
statements;
}

Note: function definition in javascript we write either in head section or
in body section.
but function definition execution only possible through function calling


function call: function call in javascript invokes function definition .
syntax:
 functionname();

 or

 using event trigger mechanism to invoke the function definition.


 Example program on function using event trigger mechanism:
 ----------------------------------------------------------
 <html>
<head>
<script type="text/javascript">
function display()
{
document.write("welcome to javascript functions"+"<br>");
document.write("function definition");
}
</script>
</head>
<body>
<form>
<input type="button" value="submit" onclick="display()">
</form>
</body>
</html>


Note: in the above example onclick is an event , similerly
javscript support many event handling mechanisms they are
--> onclick
-->ondblclick
-->onmouseover
-->onmouseout
->onload .....
etc


Example program on function calling:
----------------------------------------------------------
<html>
<head>
<script type="text/javascript">
function display()
{
document.write("welcome to javascript functions"+"<br>");
document.write("function definition");
}
display();
</script>
</head>
<body>

</body>
</html>


Example program on function with parameters:
--------------------------------------------------
<html>
<head>
<script type="text/javascript">
function display(name,age)
{
document.write("name is=  "+name+"  age is"+age);
}
</script>
</head>
<body>
<form>
<input type="button" value="submit" onclick="display('shravan',28)"/>
</form>
</body>
</html>


example2:
----------------
<html>
<head>
<script type="text/javascript">
function display(name,age)
{
document.write("name is=  "+name+"  age is"+age);
}
display('timeberner',56);
</script>
</head>
<body>

</body>
</html>


Javascript display possibilities:
--------------------------------------------
in javascript to display content we follows the gien ways.

1) Writing into an HTML using innerHTML
2) Writing into an HTMl using document object
3) using window.alert()
4) using console.log()


1. Using InnerHTML:
------------------------
<html>
<head>
</head>
<body>

<h2>Using innerHTMl </h2>
<p id="demo">getElement ById method we are using</p>
<button type="button" onclick='document.getElementById("demo").innerHTML="Hello javscript!"'>
click here</button>


</body>
</html>


2)Using document.write()
---------------------------------------------
<html>
<head>
<script type="text/javascript">
function display()
{
document.write("welcome to javascript functions"+"<br>");
document.write("function definition");
}
display();
</script>
</head>
<body>

</body>
</html>


3)using window.alert()
------------------------------------
<html>
<head>
</head>
<body>
<script type="text/javascript">
window.alert("window alert method in  javscript");
</script>
</body>
</html>


4)using console.log()
--------------------------------------------------
Note: in javscript using console object we print the javascript code
on console scree.
in the following example using log method to print text on console screen....


<html>
<head>
</head>
<body>
<script type="text/javascript">
console.log("welcome to console part");
console.log("console related output");
</script>
</body>
</html>


Ways to embedded javscript code in HTML:
------------------------------------------------------------

To embedded script code in html we follows the given ways.
1. body
2. head
3. using external file


3. Using External file:
-------------------------------------------
In javascript using external file to include the code,
in the following examples are included javascript code in external file

Test.js
---------------------------
<html>
<head>
<script src="extern.js" type="text/javascript" >
</script>
</head>
<body>
<input type="button" value="click" onclick="display()"/>
</body>
</html>


extern.js
---------------------------------------
function display()
{
window.alert("external js file");
}

Note: In external file inclusion in javascript both file must be
included in the same location.


ECMA2015 OR ES6 standard javascript includes these below features.

let & var keyword:
-------------------------------------------


<html>
<head>
</head>
<body>
<script language="javascript">
function display()
{
for(let i=0;i<=5;i++)
{
console.log(i);
}
}
display();
</script>
</body>
</html>


Ex2:
---------------
<html>
<head>
</head>
<body>
<script language="javascript">
function display()
{
for(let i=0;i<=5;i++)
{
console.log(i);//scope of the i variable only inside
}
console.log(i);//outside scope of the let keyword
}
display();
</script>
</body>
</html>


Uncaught ReferenceError: i is not defined
    at display (Test.html:12)
    at Test.html:

Examle program on var keyword:
---------------------------------
<html>
<head>
</head>
<body>
<script language="javascript">
function display()
{
for(var i=0;i<=5;i++)
{
console.log(i);
}
console.log(i);
}
display();
</script>
</body>
</html>

Note: The scope of the var keyword exist outside of the method also.


const keyword:
-----------------------------------------
<html>
<head>
</head>
<body>
<script language="javascript">
const a=10;
console.log("a value is"+a);
</script>
</body>
</html>


ex2:
---------------
<html>
<head>
</head>
<body>
<script language="javascript">
const a;
a=10;
console.log("a value is"+a);
</script>
</body>
</html>

Uncaught SyntaxError: Missing initializer in const declaration


Arrow function :
-------------------------------------------
Arrow function in javascrit follows with a different syntax:
equal sign before of the parenthesis and after paraenthesis arrow sign
Arros function concept executed by fast by the engine.


<html>
<head>
</head>
<body>
<script language="javascript">
const display=()=>
{
for(var i=0;i<=5;i++)
{
console.log(i);
}
}
display();
</script>
</body>
</html>


this keyword:
----------------------------------------
here this is a keyword, in javascrit this keyword referes
to the global object by default i.e

it referes window object
object contais(properties and methods)


<html>
<head>
</head>
<body>
<script language="javascript">
console.log(this);
</script>
</body>
</html>

output: window


<html>
<head>
</head>
<body>
<script language="javascript">
document.write(this);
</script>
</body>
</html>

window object


Declare this keyword in normal function:
---------------------------------------------

<html>
<head>
</head>
<body>
<script language="javascript">
function display()
{
document.write(2+2+"<br>");
document.write(this);
}
display();
</script>
</body>
</html>


return: global object i.e window


Example program on this keyword declared in Object:
-------------------------------------------------------
whenever we declare this keyword inside of any
object in that case this keyword return only that object
related data only.


<html>
<head>
</head>
<body>
<script language="javascript">
const hello=
{
name:"shravan",
sum: function(){
console.log(2+2);
console.log(this);
}
}
hello.sum();
</script>
</body>
</html>


javascript objects:
-------------------------------------------------
A javascript object is an entity has state and it's behaviour
(properties and methods)
--> it is not a class based language .

In java how we create Object:
  first we create class
  after that we create object

  In javascript class doesn't exist
  we create directly Object

  Note: we don't create any class, but we will create object directly.


  How many ways we create Object in javascript:
  --------------------------------------------
  Here in javascript object creattion is mainly follows in 3 ways.

  1) By using Object literals
  2) By using instance of an Object
  3) By using Object  constructor


  1. By using Object Literals:
  -----------------------------------
  In javascript object literal follows the given syntx:
  Object ={Property1: value1,property2:value2................}


 <html>
<head>
</head>
<body>
<script language="javascript">

employee={id:100,name:"shravan"}
document.write(employee.id+"  "+employee.name);
</script>
</body>
</html>


 2) By Using Object Instance:
 -----------------------------------------
 syntax:
 var objectname=new Object();

 <html>
<head>
</head>
<body>
<script language="javascript">

var student=new Object();
student.id=101;
student.name="shravan";
student.address="hyderabad";
document.write(student.id+" "+student.name+" "+student.address);

</script>
</body>
</html>


3) By using Object constructor:
----------------------------------------------
<html>
<head>
</head>
<body>
<script language="javascript">

function student(id,name,address)
{
this.id=id;
this.name=name;
this.address=address;
}
s=new student(11,"Akshay","nagpur");
document.write(s.id+" "+s.name+" "+s.address);
</script>
</body>
</html>


Builtin methof of an Object:
-----------------------------------
1. assign()
2.is()
3. freeze()
4.isfrozen()


Example program on Object.assign() method:
---------------------------------------------------

<html>
<head>
</head>
<body>
<script language="javascript">
var o1={a: 1,b: 4,c:5};
var o3={d:1,e:2,f:3};
var o2=Object.assign({c:4,d:8},o1);
document.write(o2.a+" "+o2.b+"  "+o2.c+" "+o2.d);
                 1       4        5        8
</script>
</body>
</html>


Example program on is() emthod in javascript:
----------------------------------------------------------
Object.is() method used to determine whether two values
are same values or not.


<html>
<head>
</head>
<body>
<h2>Object.is() method in javascript</h2>
<script language="javascript">
document.write(Object.is('Hello','Hello')+"<br>");
document.write(Object.is('Hello','World')+"<br>");
document.write(Object.is(null,null)+"<br>");
document.write(Object.is('Hello','hello'));

</script>
</body>
</html>


Example program on freeze();
--------------------------------------------
when we apply freeze( ) method for any perticular object
then taht object values doesn't modify or updated.

<html>
<head>
</head>
<body>

<script language="javascript">
var obj1={a:20,b:30};
var obj2=Object.freeze(obj1);
obj2.a=40;
document.write(obj2.a);


</script>
</body>
</html>


Example program on isfrozen();
-----------------------------------
Using isfrozen() method we check the objects which are in freeze state or not


<html>
<head>
</head>
<body>

<script language="javascript">
var obj1={a:20,b:30};
var obj2=Object.freeze(obj1);
document.write(Object.isFrozen(obj2));
</script>
</body>
</html>


javascrit Date:
------------------------------------------
javascript date object exist with multiple
builtin methods. using those methods we find the
date, year ,month  etc....


Date object built-in methods:
-----------------------------
getDay()
getFullYear()
getHours()
getMilliSeconds()
getMinutes()

<html>
<head>
</head>
<body>
<script language="javascript">
var date=new Date();
document.write(date.getDay()+"<br>");
document.write(date.getHours()+"<br>");

</script>
</body>
</html>


Array Object in javscript:
---------------------------------------------------
in javascript Array is an Object represetns collection of
similer type of elements.

Array Object in javascript created mainly in 3 ways:
------------------------------------------------

Those are
1. By array literal
2. By crating an instance of an array
3. by using array constructor


1. By Array Literals :
---------------------------------------
var arrayobject=[valu1,value2,...........]

<html>
<head>
</head>
<body>
<script language="javascript">
var names=["shravan","akshay","Arpit","nakul"];
for(n=0;n<names.length;n++)
{
document.write(names[n]+"<br>");
}
</script>
</body>
</html>


2. By creating an instance of an array:
----------------------------------------------

<html>
<head>
</head>
<body>
<script language="javascript">
var student=new Array();
student[0]="computers";
student[1]="electronics";
student[2]="maths";
student[3]="Civil ";
for(n=0;n<student.length;n++)
{
document.write(student[n]+"<br>");
}
</script>
</body>
</html>


3.using Array constructor
----------------------------
<html>
<head>
</head>
<body>
<script language="javascript">
var student=new Array("abc","bcd","cde");
for(n=0;n<student.length;n++)
{
document.write(student[n]+"<br>");
}

</script>
</body>
</html>


Array Methods in javacsript:
-------------------------------------
The following builtin methods supported by javascript.

1. concat()
2. filter()
3. reverse()
4. sort()


1.
<html>
<head>
</head>
<body>
<script language="javascript">
var arr1=["nakul","arpit"];
var arr2=["akshay","shravan"];
var arr3=arr1.concat(arr2);

document.write(arr3);
</script>
</body>
</html>

2.

<html>
<head>
</head>
<body>
<script language="javascript">
var salary=[2000,4000,6000,8000];
function test(sal)
{
return sal<5000;
}
document.write(salary.filter(test));

</script>
</body>
</html>


3. revers()
<html>
<head>
</head>
<body>
<script language="javascript">
var arr1=["Abc","Nbcd","Qde","Def"];
arr1.sort();
var arr2=arr1.reverse();
document.write(arr2);
</script>
</body>
</html>

4.