JavaScript Form Validation

We?re all familiar with ColdFusion?s built-in <cfform>. Some people think it?s great, as it automatically generates client side form validation. Saves you some time, as you no longer need to worry about learning JavaScript.

While that may be true, there are a number of compelling reasons to not use <cfform>

1) Every component of cfform (cfinput, cfselect) will slow down the loading of your page. ColdFusion has to parse each cfform component and convert it into ?regular? HTML, along with any JavaScript validation routines necessary.
2) The validation that you can do with cfform is somewhat limited. For example, you can determine whether or not a text input is empty?but you could not, for example, ensure that the length of the value entered was greater than 6 characters (some sites require a password be entered, with a minimum of 6 characters). Writing your own JavaScript will allow you much more flexibility in the validation that you can perform.
3) <cfform> components such as <cfinput type=?text?> are parsed into <input type=?text?> by the ColdFusion server. However, if you are writing XHTML compliant code (which you should be), you know that tags such as <input type=?text?> become self-closing (e.g. <input type=?text? />). <cfform> elements will not do this, and thus render your entire document as invalid markup.

I?ve always tried to dissuade people from using cfform and learning to write their own JavaScript. Aside from the reasons above, learning a new technology will never hurt you. Additionally, since both JavaScript and <cfscript> (as well as Flash?s ActionScript) are ECMAScript based, they share many similar properties. Learning JavaScript will make learning both <cfscript> and ActionScript much easier.

Certainly, JavaScript can be used for much more than form validation. However, this is where most people start learning it?and will allow you to start using it fairly quickly.

An Overview of JavaScript Syntax

1) All of the elements on a Web page are considered to be individual objects to JavaScript. Objects are referenced using a hierarchical dot-notation. The topmost object is the window. Within the window is the document. Within the document there may be a form, and within that form there is likely a form field. Assuming the form?s name is ?myForm?, and the form field name is ?myField?, the syntax to access the value of the form field would be:


Notice that we go from the topmost object, down to the innermost object. ?value? is obviously not an object, but a property of the innermost object that we referenced, which was the form field myField.
2) JavaScript is cAsE-sEnSiTiVe. This means if your form is named ?myForm?, you cannot reference it with window.document.myform? This will throw an error, as the form ?myform? does not exist.

This will likely be the biggest challenge you face in moving from ColdFusion to JS.

3) JavaScript has functions, which can simply be thought of as code snippets, that can be called on a particular event (onmouseover, onclick, onfocus, onblur, etc).

Here?s a quick sample of a very simple JavaScript function, which is called on the onload event (the onload event fires when a page finishes loading).

1. <html>
2. <head>
3. <title>Simple JavaScript Example</title>
4. <script language=?JavaScript? type=?text/javascript?>
5. function sayHi() {
6.     alert(?Hello! Welcome to my World!?);
7. }
8. </script>
9. </head>
11. <body onload=?sayHi();?>
13. </body>
14. </html>

What we have here is a simple Web page that will pop up a JavaScript alert box with the text ?Welcome to my World!? when the page loads.

On lines 5-7, we have our function, which is named sayHi. As with ColdFusion, functions are followed by parentheses, in order to accommodate any arguments (if they exist).

The function itself is enclosed in curly braces. This is a simple one line function, which uses the built in JavaScript alert(). Notice that the line ends with a semi-colon. While it is not mandatory in JavaScript to terminate a line with a semi-colon, it is recommended, as it is proper syntax to do so. <cfscript> adheres to this as well, but is much more strict (<cfscript> will throw an error if a line is not properly terminated?JavaScript will not).

On line 11, we have our <body> tag. Within the <body> tag, we utilize the onload event to call our function. Again, notice the case-sensitivity. The name of the function is sayHi. We call it by using sayHi. Not sayhi, Sayhi, or SayHi.

Form Validation

Let?s build a very simple form to start off with.

<form name=?myForm? method=?post? action=?page2.cfm?>
    <input type=
?text? name=?yourName? />
    <input type=
?submit? value=?proceed? />

Nothing too fancy. One simple text input, and a submit button. The only thing to note is that we gave our form a name, using the name attribute of the <form> tag.

When the user hits the ?proceed? button, the form will submit, whether the user has entered a value or not.

To prevent that from happening, let?s write our first JavaScript function.

<script language=?JavaScript? type=?text/javascript?>
function validateFields() {
    if (document.myForm.yourName.value == ??) {
        alert(?Please Enter Your Name?);

Our function (named validateFields) is enclosed in curly braces. Within the function, we have a condition. This condition references our form field (notice we don?t specify window before we specify document?specifying window is generally implicit, as all documents are assumed to be within a window?you can?t be viewing a Web page without it being in a window). document.myForm.yourName.value is whatever value the user has entered into the form field.

We use the equality comparison operator, which in JS is == (two equal signs). This is used to test for equality, where a single equal sign is used to assign values.

For example:

var myName = ?CJ?; (assignment)
if (myName == ?CJ?) ? (testing for equality)

So our condition checks to see if the value in the specified form field is blank (an empty string, indicated by ??). If the condition is met, we alert the user with a JavaScript alert() containing the message ?Please Enter Your Name?.

Now that we have a function, we need to call it on a specific event. JavaScript has an onsubmit event that pertains to a form. This is the event that we will use to call our validation function.

<form name=?myForm? method=?post? action=?page2.cfm? onsubmit=?return validateFields();?>

You may be noticing that not only are we calling the function from the onsubmit event?but we also have the word return before the name of the function. This indicates that we expect the function to return a value. In this case, we will return either true or false. A false return value will indicate that the validation criteria have not been met, and the form will not submit. A true return value will indicate that all form fields have been successfully validated, and allow the form to submit.

In order to return a value, we need to make two modifications to our function:

<script language=?JavaScript? type=?text/javascript?>
function validateFields() {
    if (document.myForm.yourName.value == ??) {
        alert(?Please Enter Your Name?);
        return false;
    return true;

Notice that within our condition, if the value of the form field is empty, we not only alert the user, but we also return false. This will prevent the form from submitting.

If the condition is not met, we return true, which allows the form to submit.

Here is the final product:


My First Form Validation</title>
<script language=?JavaScript? type=?text/javascript?>
function validateFields() {
    if (document.myForm.yourName.value == ??) {
        alert(?Please Enter Your Name?);
        return false;
return true;

<form name=?myForm? method=?post? action=?page2.cfm? onsubmit=?return validateFields();?>
    <input type=
?text? name=?yourName? />
    <input type=
?submit? value=?proceed? />


Incidentally, for forms with multiple fields (as most have), you simply put a condition for each form field in the same function. For example, if our example above contained a 2nd input, with a name of ?pword? (<input type=?text? name=?pword? />), our function would look like:

<script language=?JavaScript? type=?text/javascript?>
function validateFields() {
    if (document.myForm.yourName.value == ??) {
        alert(?Please Enter Your Name?);
        return false;
    if (document.myForm.pword.value == ??) {
        alert(?Please Enter Your Password?);
        return false;
return true;

As each condition is processed, if the validation criteria is met, the function simply moves on to the next condition. If the validation criteria is NOT met, the return false will cease processing of the function immediately.

Copy and paste this into an HTML page and you can test it out yourself. You have now successfully written your first JavaScript form field validation! Take a breath, do a victory lap?whatever feels right?and c?mon back so we can tackle a few other validations that you can add to your form. Some may be a bit more difficult than the example above?take your time, don?t get discouraged, and ask questions if you get confused! :)

Validating Text Inputs

All of the examples below will assume one form field (input type=?text?) named ?myField? within a form named ?myForm?.

1) Ensuring at least 3 characters in a field:

if (document.myForm.myField.value.length < 3) {
alert(?Not Enough Characters!?);
return false;

As in the previous example, we use hierarchical notation to ?drill down? to the form field?s value. However, now we are going to access a specific property of that value. The property in question is ?length? (which is simply appended still using dot notation).

So our condition states, ?if the length of the value of the field ?myField? in the form ?myForm? is less than 3 characters, validation fails (alert the user and return false).?

2) Ensuring no more than 6 characters in a field:

if (document.myForm.myField.value.length > 6) {
alert(?Too Many Characters!?);
return false;

Same as above, except now testing for greater than (>) as opposed to less than (<).

3) Ensuring a length between 3 and 6 characters:

if ((document.myForm.myField.value.length < 3) || (document.myForm.myField.value.length > 6)) {
alert(?Please enter a value between 3 and 6 characters?);
return false;

We are now testing for two distinct criteria. The length must NOT be less than 3, nor can it be greater than 6. We use two sets of validation criteria, each in parentheses. We use the || character in JavaScript to denote ?OR?. So literally, we are saying ?If the length of the value of the field ?myField? in the form ?myForm? is less than 3 characters OR the length of the value of the field ?myField? in the form ?myForm is greater than 3 characters, validation fails (alert the user and return false).?

4) Ensuring only a numeric value:

if (isNaN(document.myForm.myField.value)) {
alert(?Please enter a numeric value only!?);
return false;

This one is a bit different. Now we are using a built in JavaScript function, isNaN(). isNaN() stands for ?is not a number?. Like some ColdFusion functions, it accepts an argument. In this case, it?s the value to be tested?which is the value of the field named ?myField? in the form ?myForm?. If this value is not numeric, validation fails.

5) Ensuring that a value contains the ?@? character:

if (document.myForm.myField.value.indexOf(?@?) < 0) {
alert(?Please Enter a Valid E-Mail Address?);
return false;

This example uses JavaScript?s indexOf() method. A method is very similar to a function (it technically is a function within an object?but that?s more than we need to be concerned with at this point). indexOf is similar to ColdFusion?s find() function. It simply searches for the occurrence of a substring within a string. It returns the position (or index) that the character was found. Remembering that JavaScript starts counting at 0, indexOf will return a number greater than or equal to 0 if the substring is found. Otherwise, it returns ?1. So we check to see if the indexOf method returns a value less than 0. If it does, validation fails.

Validating Select Inputs

How can you make sure a user has selected a value in a <select> input? Remembering that a <select> input is made up of various <option> tags, each option is considered a position (or, more accurately, an index) within the select. Since JavaScript starts counting at 0, the very first <option> in a <select> holds position 0. Whichever option is currently selected can be ascertained with the selectedIndex property of a select field.

If the first option is selected, document.myForm.mySelect.selectedIndex will return 0.

If none are selected (possible in a <select> where multiple is enabled), selectedIndex returns ?1.

Remember? case sensitivity. The property is selectedIndex. NOT SelectedIndex or selectedindex.

<select name=?autos?>
    <option value=
??>Please Select One:</option>
    <option value=
    <option value=
    <option value=
    <option value=

Given the <select> input above, we want to ensure that the user has chosen an option other than the first one?which means we simply want to ensure that the selectedIndex is greater than 0.

if ( <= 0) {
alert(?Please Select an Auto?);
return false;

Validating Radio Buttons

Radio buttons are groups where only one of the presented choices can be selected:

The code to generate this group of radio buttons is:

<input type="radio" name="sex" value="M">Male
<input type=
"radio" name="sex" value="F">Female

Notice that the name of both radio buttons is the same (although the values differ). This is how we ensure that only one input from the group can be chosen.

Radio buttons in JavaScript are slightly more complicated than other inputs. Because they are comprised of multiple elements with same name, we cannot use the hierarchical notation that we?re used to. could refer to either one of those buttons (and as such, would throw an error). Radio button groups are actually arrays in JavaScript. Therefore, we must use array notation to reference a specific radio button. In the case of these two buttons above, each could be referenced as:[0] (remember, JavaScript starts counting at 0?so this is the ?M? value)[1] (remember, JavaScript starts counting at 0?so this is the ?F? value)

Radio buttons possess a ?checked? property that is either true or false, depending on the state of the button. In order to ensure that the user has checked one of the radio buttons within the group, it becomes necessary to loop over the group:

1. var howMany = 0;
3. for (var i=0; i<; i++) {
4.     if ([i].checked == true) {
5.         howMany++;
6.         break;
7.     }
8. }
10. if (howMany == 0) {
11.     alert(?Please Indicate Your Sex?);
12.     return false;
13. }

Now, I know what you?re saying. ?Whoa?CJ?you went and got funky on me.? Well yes, admittedly, it?s a little funky. But that?s ok?we can de-funk it easily enough.

Line 1: sets a variable called howMany, with an initial value of 0. This will ultimately be the number of checked radio buttons.

Line 3: This is a loop in JavaScript. It?s very similar to a loop in <cfscript>, and not terribly different than a loop in CF once it?s been dissected.

We start with a loop index of i. i starts off as 0 (var i=0), and increases by one for each iteration of the loop (i++). The loop will continue to iterate while i is less than the length of the radio button array. Since this particular radio button array only has two items (male or female), the loop will iterate twice.

Line 4: Uses array notation to check a specific radio button within the group. Specifically, it is looking to see if that specific radio button is checked. If it is, proceed to line 5.

Line 5: Use the JavaScript notation to increment a value (the double plus sign) to increment the value of the variable howMany.

Line 6: Because we have encountered a checked button, which was our goal, there is no reason to continue looping through the remainder of the buttons. We can simply break out of the loop.

Line 10: Once the loop is finished (whether it looped over each element, or was broken out of), check the value of the variable howMany. If it still equals 0, no radio buttons have been checked. If this is the case, validation fails. Proceed to line 11.

Line 11: Validation failed. Send an alert() message to the user, and return false on Line 12.

This might take some going over to get used to, but once you understand the concept of the radio button group being an array, and looping over the elements in the array, it will be very clear.

Well, I?m going to leave you there. It?s a lot of new information to take in in one sitting. Hopefully you feel that you have a better familiarity with JavaScript and form field validation?and you?ll pursue it to the point where you can start writing your own validation routines.

To see one single form that holds all of the examples above, please visit View the source for a full understanding.

I would like to suggest a few other resources that might help as well:

The JavaScript Bible, by Danny Goodman. Mr. Goodman is thought of as *the* definitive JavaScript authority (and with good reason). This book will teach the most basic beginner, and remain a valuable reference to the most seasoned JS pro. It?s not so technical that it?s impossible to understand?yet it?s not dumbed down to the point where it fails to teach.
This site offers a number of different teachings on a number of different subjects. I can?t speak for the others, but I?ve found their JS section to be very helpful.

qForms JavaScript API
Dan Switzer has put together a fantastic JavaScript API for interacting with forms. While I believe that it?s always beneficial to know how to write your own code, there?s nothing wrong with saving some time once you know how. Dan?s qForms are free?easy to work with?and will let you easily manipulate your forms. Not only for form validation, but dynamic drop downs as well (two or more related selects). Check it out!

The forums! Yes, we?re a CF community, but in our daily dealings with CF, we have to wander into other areas as well. Whether it be SQL, HTML, XHTML, JavaScript, CSS, etc?we touch it all. So please feel free to ask your JS related questions! I?ll do my best to answer as many of them as I can :)


About This Tutorial
Author: Charlie Griefer (CJ)
Skill Level: Intermediate 
Platforms Tested: CF5,CFMX
Total Views: 146,728
Submission Date: August 14, 2003
Last Update Date: June 05, 2009
All Tutorials By This Autor: 15
Discuss This Tutorial
  • I'm having a major headache in here (thanks to my brainwrecking take home quiz), trying to decipher various validation JavaScript codes I downloaded from the net. I'm a javascript novice of a couple of weeks and stumbling on this page is very rewarding. Thank you very much! More power to you!

  • i am the beginer of javascript leaner....this artical is fine to learning javascript basics..........

  • How do you create an event handler should confirm whether the user wants to change their selection (Select Box). If the user clicks "Cancel" to indicate they do not want to change their selection, the previously selected option should remain selected.

  • asdfasdf

  • Hi Charlie EXCELLENT tutorial. I have been using it and as well as improving my JS skills I have found it bulletproof and if followed properly it cannot fail. One thing i did add to make the whole process more efficient was to ad a focus line so that when the person filling out the form makes an error they are redirected back to the form input area in where they made that error. the line i added was: document.form1.contact_name.focus(); it is added to the statement as in the following example: if (document.form1.contact_name.value==""){ alert('Please Enter Your Contact Name'); document.form1.contact_name.focus(); return false; } Thanks again for a great tutorial cheers Grabit

  • Mr. Griefer: I implemented your javascript and it is now successfully validating the text box and the select drop-down box ! Thanks ! I want to use a form called myform so the user enters in the data (text and select box), the javascript validates user input for the input and select fields, and then the user re-enters the data and the user selects a submit button and a next web page is displayed (p22.cfm see below). Below is the form statement and input submit statement that I am attempting to use:

    The form and submit statements are causing the p22.cfm page to immediately display after validating the text field once. Is there another way to write the form and submit statements so that the user enters in the data, all fields are validated, the user corrects his data submission, selects the submit button, and the p22.cfm page is displayed ? I am not all that familiar with the onsubmit option. thanks, Ed

  • Sir: I have to perform data validation on a html form drop-down select field. I am using CF to populate the select drop-down box with entries. I want to implement the data validation via javascript using the onsubmit option of a form submit button. I have successfully implemented your javascript to validate regular text fields:


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