Slide 12.14: JavaScript functions

JavaScript Functions

To keep the browser from executing a script as soon as the page is loaded, you can write your script as a function. Functions are defined at the beginning of a page, in the <head> section.

The script below uses two methods of the object String to check the alphabetic name:

 function name( var1, var2, ..., varX ) {
   some code
 }

The method indexOf(value [,from]) returns the index within the calling String object of the first occurrence of the specified value, starting the search at from, or -1 if the value is not found.

The method charAt returns the specified character from the string.

There are two kinds of variables:

Local variables: If you declare a variable, using var, within a function, the variable can only be accessed within that function. When you exit the function, the variable is destroyed.

Global variables: If you declare a variable outside a function, all the functions on your page can access it. The lifetime of these variables starts when they are declared, and ends when the page is closed.

Demonstration
The following demonstration shows how the script of HTML and JavaScript is displayed on the Web.


<html> <head> <script type="text/javascript"> function myfunction( txt ) { alert( txt ); } </script> </head> <body> <form> <input type="button" onclick="myfunction('Good Morning!')" value="In the Morning" /> <input type="button" onclick="myfunction('Good Evening!')" value="In the Evening" /> </form> <p> When you click on one of the buttons, a function will be called. The function will alert the argument that is passed to it. </p> </body> </html>