Insertion of javascript in html,comments in javascript , function of javascript, javascript functions
Comments in javascript
Comments are
non-executable statement inn program .comments are used to provide information or
explanation about programming construct .statement added in comments are ignored
by javascript . it supports two types of comments.
1.single line
comment (//…….):
Single line
comment begins with //.
The javascript
ignores everything from // to the end of the line .
2.multiple comments :
Multiple comments
are used to comment on more then one line .
It starts
with /* and ends with */.
Commonly used built-in function in javascript
Function is
used to perform repetitive tasks whenever required . it is reusable
code-block that will be executed when it
is called.
·
parseInt()
:this function
is used to parse a string and convert it into a number.
·
parseFloat():
this function
is used to parse a string and convert it
into floating point representation.
·
Alert(): this function displays alert popup box with ok button . this is also called as a message box.
·
Prompt():this function is used when you want to input value from user at
time of program execution . it displays
ok and cancel buttons. ok button returns input value,cancle button returns null value.
·
Confirm():this function displays confirmation
message box with ok and cancel button . ok button returns ‘true’ and cancel
buttons returns ‘false’.
·
To lowercase (): this string functions used to convert the given
string into lower case alphabets .
·
To uppercase():this string functions used to convert the given
string into upper case alphabets .
·
Is NaN(): it returns ‘true ‘is given value is not a
number .
·
It
returns’ false’ if given value is number.
Example program is as follows
Input:-
<!doctype html>
<html>
<head>
<title>area of
circle</title>
</head>
<body bgcolor=gold>
<h1>program to calculate
area of circle</h1>
<script
language="javascript">
var r ,area;
r=prompt("enter the
radius of circle");
area=3.14*r*r;
document.write("<h1>you
entered radius value:</h1>"+r);
document.write("<h1>area
of circle:</h1>"+area);
</script>
</body>
</html>
Output:-
Comments