246996016-HTML5-Step-by-Step

300 Chapter 16
Validating a Web Form with jQuery and JavaScript
One typical use of JavaScript is to validate a Web form, or more appropriately, prevalidate
a Web form. When a Web form is submitted, it is sent to a server-based program
which can then do something useful with the data, such as complete an order, or store
the data in a database. However, using JavaScript for validation provides no security for
the server-based program.
Don’t Substitute JavaScript Validation for Server-Side Validation
There is no guarantee that the visitor to your Web page has JavaScript enabled in
their browser. Therefore, you cannot rely on JavaScript as the sole means to verify
that the user has entered properly formatted data. More than one Web site has
been hacked because the programmer relied solely on JavaScript to validate and
verify the contents of user input from a Web form.
All data must be verified at the server or within the server code. No amount of
JavaScript validation, trying to require JavaScript, or other tricks will ensure that the
data is safe. Always verify data at the server. When used as a means to validate form
data, JavaScript is to be used only to enhance the user experience by providing
early feedback on known invalid data. JavaScript is never—and should never be—
used to truly test whether the data is valid.
With that in mind, here’s a simple form and some JavaScript/jQuery code to validate the
text box on the form:
jQuery 101
Answer:
$("#myForm").submit(function() {
if ($("#firstName").val() == "Yes") {
alert("Form entered correctly");
} else {
alert("Form not correct");
return false;
}