Data Validation
Unlike other scripting languages such as VBScript, JavaScript
does not include a substantial list of pre-defined functions
for data manipulation such as checking for valid dates or formatting
dates, etc.... Therefore we must either write them ourselves
or find a reliable source for pre-written functions.
We can then incorporate these functions into our scripts
as in the following example (leftTrim is a function that has
been written in JavaScript).
function
MyForm_onSubmit() {
var bnSuccess = true;
var strErrors = "";
if(leftTrim(document.MyForm.FName.value)
.length==0) {
strErrors = "\n First Name";
bnSuccess = false;
}
if(leftTrim(document.MyForm.LName.value)
.length==0) {
strErrors = strErrors + "\n Last Name";
bnSuccess = false;
}
if (leftTrim(document.MyForm.CName.value)
.length==0) {
strErrors = strErrors + "\n City Name";
bnSuccess = false;
}
if (bnSuccess ==
false) {
alert("This form has errors on the"+
"following items"+strErrors+
"\n\nPlease correct these
errors"+
"before submitting form.");
}
return bnSuccess;
}
In the above example, the variable "bnSuccess" is used to
track if an error exits and conditionally display an error message.
The value is then returned to the form, which if the value is
false will cause the form submission to be canceled.
The variable "strErrors" is used to accumulate a list of
errors which is inserted into the error message letting the
user know what is wrong with the form values. The "\n"
is a special line break or new line character that can be inserted
into a JavaScript string (a collection of characters or text).
This will work like a carriage return on a typewriter.
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