JavaScript/Java Script Basics.html at main · Varanasi-Software-Junction/JavaScript · GitHub

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Javascript Basics-1
Javascript is a scripting language which runs inside a web browser. It was developed by Netscape Navigator.

Javascript is an Object Oriented Language with automatic type conversion and doesn’t require variable declaration before use.

To run Javascript you need create a html page and add the Javascript within
<script>

//Write script here

</script>


To start with, just write alert(“Hello”); inside a Javascript script tag and load the page.

Here is the complete code.

<!DOCTYPE html>

<html>
<head>
<meta charset="UTF-8">
<title>Alert</title>
<script>
alert("Hello");


</script>
</head>
<body>

</body>
</html>


Javascript has the following data types.

Javascript provides event handlers for reacting to different events like click, mouse move, key press,etc

Javascript also provides methods for accessing elements in the html document via the methods of the document object.
document.getElementbyId(id) returns a single object. Returns null if the element doesn’t exist.

document.getElementsByName(name) returns an array of elements. It returns an array of 0 length if the name does not exist.

document.getElementsByTagName(tagname) returns an array of elements of the given tag. For example

document.getElementsByTagName(“p”) would return an array of paragraphs.

Lastly, we have a document.getElementsByClassName that searches on the basis of css classes

Examples
This will swap contents of the 2 textboxes.
<!DOCTYPE html>

<html>
<head>
<meta charset="UTF-8">
<title>Id</title>
<script>
function doSwap()
{
var x=document.getElementById("ta");
var y=document.getElementById("tb");
var t=x.value;
x.value=y.value;
y.value=t;
}
</script>
</head>
<body>
A<input type="text" id="ta"/>
<br/>
B<input type="text" id="tb"/>
<br/>
<input type="button" onclick="doSwap()" value="Swap"/>
</body>
</html>
Elements By Name

This will uncheck each and every Radio Button.
<!DOCTYPE html>

<html>
<head>
<meta charset="UTF-8">
<title>Name</title>
<script>
function doCheckAll()
{

var radiobuttons=document.getElementsByName("game");
var n=radiobuttons.length;
for(var i=0;i<=n-1;i++)
{
radiobuttons[i].checked="";


}
}
</script>
</head>
<body>
A<input type="radio" name="game"/>
<br/>
B<input type="radio" name="game"/>
<br/>
C<input type="radio" name="game"/>
<br/>
D<input type="radio" name="game"/>
<br/>
E<input type="radio" name="game"/>
<br/>
F<input type="radio" name="game"/>
<br/>
<input type="button" onclick="doCheckAll()" value="UnCheck"/>
</body>
</html>


GetElementsByClassName
Search elements by css classname

<!DOCTYPE html>

<html>
<head>
<meta charset="UTF-8">
<title>Class Name</title>
<style>
.blue
{
background-color: blue;

}
.green
{
background-color: green;

}
</style>
<script>
function traverse()
{

var textboxes=document.getElementsByClassName("blue");
var n=textboxes.length;
for(var i=0;i<=n-1;i++)
{
textboxes[i].value="Blue";


}
textboxes=document.getElementsByClassName("green");
var n=textboxes.length;
for(var i=0;i<=n-1;i++)
{
textboxes[i].value="Green";


}
}
</script>
</head>
<body>
A<input type="text" class="blue"/>
<br/>
B<input type="text" class="green"/>
<br/>
C<input type="text" class="blue"/>
<br/>
D<input type="text" class="green"/>
<br/>
E<input type="text" class="blue"/>
<br/>
F<input type="text" class="blue"/>
<br/>
<input type="button" onclick="traverse()" value="Traverse"/>
</body>
</html>

&nbsp;
GetElementsByTagName

search elements by tag name

<!DOCTYPE html>

<html>
<head>
<meta charset="UTF-8">
<title>Tag Name</title>
<style>
.blue
{
background-color: blue;

}
.green
{
background-color: green;

}
</style>
<script>
function traverse()
{

var elements=document.getElementsByTagName("div");
var n=elements.length;
for(var i=0;i<=n-1;i++)
{
elements[i].innerHTML="Div";


}
var elements=document.getElementsByTagName("p");
var n=elements.length;
for(var i=0;i<=n-1;i++)
{
elements[i].innerHTML="Paragraph";


}
}
</script>
</head>
<body>
A<div></div>
<br/>
B<p></p>
<br/>
C<div></div>
<br/>
D<p></p>
<br/>
E<div></div>
<br/>
F<p></p>
<br/>
<input type="button" onclick="traverse()" value="Traverse"/>
</body>
</html>