DAY - 9
JAVA SCRIPT FUNCTION
Ø A Javascript function is a block of code designed to
perform a particular task.
Ø A function is a group of reusable code which can be called
anywhere in your program. This eliminates the need of writing the same code
again and again. It helps programmers in writing modular codes.
Ø Functions allow a programmer to divide a big program
into a number of small and manageable functions.
Ø JavaScript function is executed when something invokes
(calls) it.
JavaScript Function Syntax
A JavaScriptfunction is defined with the function keyword, followed by a name(unique function name), a list
of parameters (that might be empty), and a statement block surrounded by curly
braces.
Syntax
The basic syntax is shown
here.
<scripttype="text/javascript">
<!--
functionfunctionname(parameter-list)
{
statements
}
//-->
</script>
Example
It defines a function
called sayHello that takes no parameters −
<scripttype="text/javascript">
<!--
functionsayHello()
{
alert("Hello there");
}
//-->
</script>
Function Parameters
Function may have parameters
and these different parameters are passed while calling a function.
These passed parameters
can be captured inside the function and any manipulation can be done over those
parameters.
A function can take
multiple parameters separated by comma.
Example
The sayHello function takes two
parameters.
<html>
<head>
<scripttype="text/javascript">
functionsayHello(name, age)
{
document.write(name +" is "+ age +" years old.");
}
</script>
</head>
<body>
<p>Click the following
button to call the function</p>
<form>
<inputtype="button"onclick="sayHello('Zara',7)"value="Say Hello">
</form>
<p>Use different parameters
inside the function and then try...</p>
</body>
</html>
The return Statement
A JavaScript function can
have an optional return statement.
This is required to return a value from
a function. This statement should be the last statement in a function.
Example
It defines a function that
takes two parameters and concatenates them before returning the resultant in
the calling program.
<html>
<head>
<scripttype="text/javascript">
function concatenate(first, last)
{
var full;
full= first + last;
return full;
}
functionsecondFunction()
{
var result;
result= concatenate('Zara','Ali');
document.write(result );
}
</script>
</head>
<body>
<p>Click the following
button to call the function</p>
<form>
<inputtype="button"onclick="secondFunction()"value="Call
Function">
</form>
<p>Use different parameters
inside the function and then try...</p>
</body>
</html>
Note:
Ø In JAVASCRIPT, functions are objects.
Ø JAVASCRIPT functions have properties and methods.
Ø In JAVASCRIPT, functions can be used as variables.
Ø Variables declared within a JAVASCRIPT function,
become LOCAL to the function. The local variables are deleted when the function
is completed.
Ø Variables declared outside a JAVASCRIPT function,
become GLOBAL to the function. Global variables are deleted when you close the
page.
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