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   ► KBWebsite Scri...JavaScript a...Beginners Co...   Print This     
  From the October 2015 Issue of Prestwood eMag
JavaScript Beginners Corner:
Validating Form Fields
Posted 12 years ago on 3/2/2008 and updated 7/6/2008
Take Away: Adding JavaScript to your HTML forms to validate form fields.


Getting Started

If you are brand new tothe JavaScript event model, you might wish to read our introduction to the JavaScript event model tutorial:

Checking if a field is blank

For this example we'll use the document object model to check a checkbox.

Key Points

  • Name the form (in this first example, we named the form Example1. You do this so you can use dot notation to refer to "theForm.theField.value".
  • Text objects have value property you can use to check.
  • You can add an onClick JavaScript event to the form. In this case, we used the event to call a function.

Here's the function code :

function CheckFieldBlank() {
if (Example1.Field1.value == ""){
alert("It's Blank!");
} else { alert("It's not blank.");

Here's the form code:

<form method="Post" name="Example1">
<input type="text" name="Field1" size="20"> 
<input type="button" value="Check If Blank" 

Checking if a field has a specific value

One more example. This example show how to check for a specific value. In this case we check for the value 'Mike' in the field.

Here's the function:

function CheckFieldMike() {
if (Example2.Field1.value == "Mike"){
alert("It's Mike!");
} else { alert("It's not Mike.");

Here's the form code:

<form method="Post" name="Example2">
<input type="text" name="Field1" size="20"> 
<input type="button" 
value="Check If Blank" onclick="CheckFieldMike();">

Here's the working sample:

  • [Load Demo] - Remember, you can view the source of browser-side JavaScript.

What's Next

Now that you know how to add JavaScript to your HTML pages and a bit about the JavaScript event model, it's time to explore the various capabilities of JavaScript. Try adding a few scripts to your HTML pages fromt his website. As you do, study in detail each script you add to your pages.


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Article Contributed By Mike Prestwood:

Mike Prestwood is a drummer, an author, and creator of the PrestwoodBoards online community. He is the President & CEO of Prestwood IT Solutions. Prestwood IT provides Coding, Website, and Computer Tech services. Mike has authored 6 computer books and over 1,200 articles. As a drummer, he maintains and has authored 3 drum books. If you have a project you wish to discuss with Mike, you can send him a private message through his PrestwoodBoards home page or call him 9AM to 4PM PST at 916-726-5675 x205.

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