Creating your own field properties
In browsers later than Internet Explorer 4, Opera 5 and Netscape 6 you can assign your own attributes to elements and then refer to their values in your JavaScript functions. Take the following input element as an example:
<input name="HomeTown" type="text" size="15" errorMsg="You need to enter a value in the Home Town field" required>
You should recognise the first three attributes as being standard HTML. The next two aren't and have been made up. They are used in the following example of how to validate fields. We could create a function that looped through all elements on a form and used the getAttribute method to check whether it was required and then if empty returned the error message.
function validateRequiredFields(){
var frm = document.forms[0];
with (frm) {
for (var i=0; i < elements.length; i++) {
if ( elements[i].getAttribute('required') != null ) {
if ( elements[i].value == '') {
alert( elements[i].getAttribute('errorMsg') );
elements[i].focus();
return false;
}
}
}
}
return true;
}Can you see how useful this could be yet? No!? Well, let's take a look at another example and see if you can't be swayed. Let's say that lots of the fields on your form need a help function. Why not add an attribute called "help" to each of the fields and then use the getAttribute method again. Consider the following field:<input name="HomeTown" type="text" size="15" help="Enter the name of the town in which you were born" />
Now we have a method for the user to receive help. Let's put a little question mark link, next to the input box for the user to click when they need help:
| Name | ? |
| Phone | ? |
| Home Town | ? |
Adding these properties to fields is as easy as creating hidden fields, in that we simply add them to the HTML Attributes as below:
The little query characters next to each field call the following JavaScript function, passing in to it the name of the field we want help with:
function getFieldHelp( fldName ) {
var fld = eval("document.forms[0]." + fldName );
if ( fld == null )
return alert('Field of that name cannot be found');
var hlp = fld.getAttribute('help');
if ( hlp == null || hlp == "")
return alert('No help has been defined for this field');
alert( hlp );
fld.focus();
}Whilst the above two examples are helpful in their own ways (well, I think so anyway ;-), hopefully they demonstrate how we can use the getAttribute method with other HTML elements to make them a lot more powerful and give us lots more options when working with JavaScript.You can read more about this method (and its counterpart setAttibute) here.
Note: In IE5.5, which has better support for the DOM standards, you can replace this line:
var fld = eval("document.forms[0]." + fldName );
with this one:
var fld = document.getElementById( fldName );
An awful lot easier. This method is also supported in Opera 5 Netsape 6 ;-) and makes getting a handle on elements on your document a doddle.
