Chapter 3

Validating Form Data


Bullet Validating data in the browser and on the server

Bullet Making a field mandatory

Bullet Setting restrictions on form fields

Bullet Practicing good data hygiene

Garbage in, garbage out. Or rather more felicitously: The tree of nonsense is watered with error, and from its branches swing the pumpkins of disaster.


In the old computing axiom of garbage in, garbage out (GIGO), or if in your genes or heart you’re British, rubbish in, rubbish out (yes, RIRO), lies a cautionary tale. If the data that goes into a system is inaccurate, incomplete, incompatible, or in some other way invalid, the information that comes out of that system will be outdated, outlandish, outrageous, or just outright wrong. What does this have to do with you as a web developer? Plenty, because it’s your job to make sure that the data the user enters into a form is accurate, complete, and compatible with your system.

In a word, you have to make sure the data is valid. If that sounds like a lot of work, I have some happy news for you: HTML has data validation baked in, so you ...

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