| Defining function | Calling function |
Functions are one of the very important features in JavaScript. A Function is a set of JavaScript statements kept together. Before you call a function, you must first define it. When you call a function, you execute the javascript statements in that function. You can pass values or parameters also to a function.
Javascript – Defining functions
Generally, functions are defined between the <HEAD> and </HEAD> tags of a HTML file. This makes sure that all functions are defined before any content is displayed. You can also place all of your functions into a separate file, and include them in a page using the SRC attribute of the SCRIPT tag.
A function definition has :
- The function keyword
- A function name
- A comma-separated list of arguments to the function in parentheses
- Statements in the functioning curly braces
General Format:
function Name(arguments)
{
statement1;
statement2;
.
.
.
statementn;
}
A function need not have arguments.
Eg.1 A function without parameters
function TestFunction1() {
 document.write(“I am a function. I have no parameters :(“);
}
Eg2: A function With parameters
function TestFunction2(name,address) {
 document.write(“I am a function. I have 2 parameters !”);
alert(‘Name: ‘ + name + ‘, Address:’ + address);
}
Javascript – Calling functions
 You call a function simply by specifying its name followed by a parenthetical list of arguments, if any:
eg1
TestFunction1()
eg2:
TestFunction1(‘tom’,’mytown, New York,NY’)
Example:
<html>
<script language=”JavaScript”>
<!– hide
function TestFunction1() {
   document.write(“I am a function. I have no parameters :(“);
}
function TestFunction2(name,address) {
   document.write(“I am a function. I have 2 parameters !”);
   document.write(‘Name: ‘ + name + ‘, Address:’ + address);
}
// Call TestFunction1
TestFunction1();
// Call TestFunction2
TestFunction2(‘tom’,’mytown, New York,NY’)
// –>
</script>
</html>
Output:
I am a function. I have no parameters 🙁
I am a function. I have 2 parameters !
Name: Tom, Address: mytown, New York,NY