Java script

JavaScript - Syntax
JavaScriptcan be implementedusingJavaScriptstatementsthatare placedwithinthe <script>...
</script> HTML tags in a webpage.
youcan place the <script> tags,containingyourJavaScript,anywhere withinyouwebpage,butitis
normallyrecommendedthatyoushouldkeepitwithinthe <head>tags.
Helloworldin JavaScript
<html>
<body>
<script language="javascript"type="text/javascript">
document.write("HelloWorld!")
</script>
</body>
</html>
Case Sensitivity
JavaScript is a case-sensitive language. This means that the language keywords, variables,
function names, and any other identifiers must always be typed with a consistent capitalization of
letters.
Comments in JavaScript
JavaScript supports both C-style and C++-style comments, Thus −

 Any text between a // and the end of a line is treated as a comment and is ignored by
JavaScript.
 Any text between the characters /* and */ is treated as a comment. This may span
multiple lines.
 JavaScript also recognizes the HTML comment opening sequence  is not recognized by JavaScript so it should be
written as //-->.
JavaScript Output
JavaScript can "display" data in different ways:
 Writing into an alert box, using window.alert().
 Writing into the HTML output using document.write().
 Writing into an HTML element, using innerHTML.
 Writing into the browser console, using console.log().
***Writing into an alert box, using window.alert().
<!DOCTYPE html>
<html>
<body>
<h1>My First Web Page</h1>
<p>My first paragraph.</p>
<script>
window.alert(5 + 6);
</script>
</body>
</html>

Using document.write()
<!DOCTYPE html>
<html>
<body>
<p>My first paragraph.</p>
<script>
document.write(5 + 6);
</script>
</body>
</html>
Using innerHTML
<!DOCTYPE html>
<html>
<body>
<p>My First Paragraph</p>
<p id="demo"></p>
<script>
document.getElementById("demo").innerHTML = 5 + 6;
</script>
</body>
</html>

What Is a Regular Expression?
A regular expression is a sequence of characters that forms a search pattern.
When you search for data in a text, you can use this search pattern to describe what you are
searching for.
A regular expression can be a single character, or a more complicated pattern.
Regular expressions can be used to perform all types of text search and text replace operations.
JavaScript Form Validation
HTML form validation can be done by a JavaScript.
If a form field (fname) is empty, this function alerts a message, and returns false, to prevent the
form from being
function validateForm() {
var x = document.forms["myForm"]["fname"].value;
if (x == null || x == "") {
alert("Name must be filledout");
return false;
}
}
<!DOCTYPE html>
<html>
<body>

<form action="demo_form.asp" method="post">
<input type="text"name="fname" required>
<input type="submit"value="Submit">
</form>
<p>If you clicksubmit, without fillingout the text field,
your browser will display an error message.</p>
</body>
</html>
Basic FormValidation
<script type="text/javascript">
<!--

// Form validation code will come here.
function validate()
{
if( document.myForm.Name.value == "" )
{
alert( "Please provide your name!" );
document.myForm.Name.focus() ;
return false;
}
if( document.myForm.EMail.value == "" )
{
alert( "Please provide your Email!" );
document.myForm.EMail.focus() ;
return false;
}
if( document.myForm.Zip.value == "" ||
isNaN( document.myForm.Zip.value ) ||
document.myForm.Zip.value.length != 5 )
{
alert( "Please provide a zip in the format #####."
);
document.myForm.Zip.focus() ;
return false;
}
if( document.myForm.Country.value == "-1" )
{
alert( "Please provide your country!" );
return false;
}
return( true );
}
//-->
</script>
Data Format Validation
<script type="text/javascript">
<!--

function validateEmail()
{
var emailID = document.myForm.EMail.value;
atpos = emailID.indexOf("@");
dotpos = emailID.lastIndexOf(".");
if (atpos < 1 || ( dotpos - atpos < 2 ))
{
alert("Please enter correct email ID")
document.myForm.EMail.focus() ;
return false;
}
return( true );
}
//-->
</script>
The checkValidity() Method
<!DOCTYPE html>
<html>
<body>
<p>Enter a number and click OK:</p>

<input id="id1" type="number" min="100" max="300">
<button onclick="myFunction()">OK</button>
<p>If the number is less than 100 or greater than 300, an error
message will be displayed.</p>
<p id="demo"></p>
<script>
function myFunction() {
var inpObj = document.getElementById("id1");
if (inpObj.checkValidity() == false) {
document.getElementById("demo").innerHTML =
inpObj.validationMessage;
} else {
document.getElementById("demo").innerHTML = "Input OK";
}
}
</script>

</body>
</html>
Changing HTML Style
<!DOCTYPE html>
<html>
<body>
<p id="p1">Hello World!</p>
<p id="p2">Hello World!</p>
<script>
document.getElementById("p2").style.color = "blue";
document.getElementById("p2").style.fontFamily = "Arial";
document.getElementById("p2").style.fontSize = "larger";
</script>
<p>The paragraph above was changed by a script.</p>
</body>
</html>

Java script

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