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Form Validation With JavaScript
Write a simple JavaScript form validator for client-side validation of user input.

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So you finally get that site of yours up and running, and sign up about fifty users for your services. You browse through the database entries, only to realize that most of the user information provided is incorrect, with email addresses that read "somewhere#something.com", telephone numbers that read "abgedaf", or birthdates saying that the applicant was born yesterday.

Where did you go wrong? The answer lies between the user submitting his or her registration, and the data reaching the database. You neglected the important intermediate step of form validation.

Today, most sites that require user input, be it for a simple mailing list or a more complex online shopping system, use form validation to cut down on instances of erroneous data entering their system. Although there is no concrete way of identifying authentic data, form validation helps identify (to a large extent) the authenticity of the type of data entered, thus cutting down on the amount of "bad" data that gets into the database.

That's where this article comes in. Over the next few pages, I'll be attempting to build a reusable library of functions for client-side form input validation, in an attempt to save you some time the next time an application needs to have its input checked for errors. The end result of this experiment will be a JavaScript object that can be easily included in your scripts, and that exposes basic object methods for data validation. It may not meet *all* your needs; however, the process should be instructive, especially if you're new to object programming in JavaScript, and you'll have very little difficulty customizing it so that it works for you.

Let's get going!

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