Form Validation
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It is usually preferred to check the input in a form when the user submits a form. Client side (browser local) validation is preferred when it can be done.  Obviously some things require databases or other server operations to correctly validate the form.

This script demonstrates a simple form validation method.

See this script in action.


<title>Form Validation Example</title>
<script language="JavaScript">

function checkRequired( theForm )
    var bMissing = false;
    // Our example just wants to make sure "something"
    //  is in the text field. Obviously you could
    //  parse the "value" property for some valid syntax.
    if ( 0 == theForm.textField.value.length )
        bMissing = true;
    //  Our example just wants to have some other item
    //  selected other than the first ("0") item.  If
    //  we had created the field so that nothing was
    //  selected the 'selectedIndex' would be (-1).
    if ( 0 == theForm.dropMenu.selectedIndex )
        bMissing = true;
    if ( bMissing )
        alert( "All form fields are required.\n"
                + "Please complete them and Submit again.");
        // false causes the form submission to be canceled
        return false;
        return true;



    Notice the "onsubmit" event handler.  It passes "this" as an
    argument which passes the form to the validation function.
<form method="GET" action="formvalidationtarget.htm" onsubmit="return checkRequired(this)">
        The rest of the form is just a couple of simple fields.
        The names or details are not important to this example.
  <p><input type="text" name="textField" size="20"><br>
  <select size="1" name="dropMenu">
    <option selected value>Select One</option>
    <option value="1">One</option>
    <option value="2">Two</option>
    <option value="3">Three</option>
  <input type="submit" value="Submit" name="submit"> <input type="reset" value="Reset"


Service Provided by Bear Consulting Group Last modified: 25 May 2009
Copyright 2001 Bear Consulting Group