Form valiation for empty data, file name
/*
Examples From
JavaScript: The Definitive Guide, Fourth Edition
Legal matters: these files were created by David Flanagan, and are
Copyright (c) 2001 by David Flanagan. You may use, study, modify, and
distribute them for any purpose. Please note that these examples are
provided "as-is" and come with no warranty of any kind.
David Flanagan
*/
<html>
<script language="JavaScript1.1">
// A utility function that returns true if a string contains only
// whitespace characters.
function isblank(s) {
for(var i = 0; i < s.length; i++) {
var c = s.charAt(i);
if ((c != ' ') && (c != '\n') && (c != '\t')) return false;
}
return true;
}
// This is the function that performs form verification. It is invoked
// from the onsubmit event handler. The handler should return whatever
// value this function returns.
function verify(f) {
var msg;
var empty_fields = "";
var errors = "";
// Loop through the elements of the form, looking for all
// text and textarea elements that don't have an "optional" property
// defined. Then, check for fields that are empty and make a list of them.
// Also, if any of these elements have a "min" or a "max" property defined,
// verify that they are numbers and in the right range.
// If the element has a "numeric" property defined, verify that
// it is a number, but don't check its range.
// Put together error messages for fields that are wrong.
for(var i = 0; i < f.length; i++) {
var e = f.elements[i];
if (((e.type == "text") || (e.type == "textarea")) && !e.optional) {
// first check if the field is empty
if ((e.value == null) || (e.value == "") || isblank(e.value)) {
empty_fields += "\n " + e.name;
continue;
}
// Now check for fields that are supposed to be numeric.
if (e.numeric || (e.min != null) || (e.max != null)) {
var v = parseFloat(e.value);
if (isNaN(v) ||
((e.min != null) && (v < e.min)) ||
((e.max != null) && (v > e.max))) {
errors += "- The field " + e.name + " must be a number";
if (e.min != null)
errors += " that is greater than " + e.min;
if (e.max != null && e.min != null)
errors += " and less than " + e.max;
else if (e.max != null)
errors += " that is less than " + e.max;
errors += ".\n";
}
}
}
}
// Now, if there were any errors, display the messages, and
// return false to prevent the form from being submitted.
// Otherwise return true.
if (!empty_fields && !errors) return true;
msg = "______________________________________________________\n\n"
msg += "The form was not submitted because of the following error(s).\n";
msg += "Please correct these error(s) and re-submit.\n";
msg += "______________________________________________________\n\n"
if (empty_fields) {
msg += "- The following required field(s) are empty:"
+ empty_fields + "\n";
if (errors) msg += "\n";
}
msg += errors;
alert(msg);
return false;
}
</script>
<!------------------------------------------------------------------------
Here's a sample form to test our verification with. Note that we
call verify() from the onsubmit event handler, and return whatever
value it returns. Also note that we use the onsubmit handler as
an opportunity to set properties of the form objects that verify()
requires for the verification process.
-------------------------------------------------------------------------->
<form onsubmit="
this.firstname.optional = true;
this.phonenumber.optional = true;
this.zip.min = 0;
this.zip.max = 99999;
return verify(this);
">
First name: <input type="text" name="firstname">
Last name: <input type="text" name="lastname"><br>
Address:<br><textarea name="address" rows="4" cols="40"></textarea><br>
Zip Code: <input type="text" name="zip"><br>
Phone Number: <input type="text" name="phonenumber"><br>
<input type="submit">
</form>
</html>
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