What's the best way to validate a form?

Megan posted this at 20:57 — 25th January 2007.

Joined: Jun 1999

I haven't done this in years and I'm not sure where to start: what's the best way to go about validating a form? I'm sure things have changed since I last attempted to do this, and I imagine a lot of instructions out there are out of date. I would like to validate about 5 fields at once, with the instructions coming up on the page somewhere.

Here is the form I am working with:

http://www.housing.uwaterloo.ca/profiles/individual.php

Do I do it all through javascript? How do I display the instructions to the user? Can I do this without event handlers in the HTML part?

Megan
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andy206uk posted this at 21:29 — 25th January 2007.

He has: 1,758 posts

Joined: Jul 2002

Megan;214050 wrote: Do I do it all through javascript? How do I display the instructions to the user? Can I do this without event handlers in the HTML part?

That's a matter of choice... usually I just check the fields using PHP as you can't rely on JS being on all for all users.

Basically you just need to check that the details being posted match what you want/expect.

For instance if you want to ensure a field is a certain size you would do:

<?php
if(strlen($_POST[varname]) < 5 || strlen($_POST[varname])  > 10) { 
    $error .= \"Varname should be between 5 and 10 characters long<br />\"; 
}
?>

Then repeat it for each variable. once you've validated all of the vars do:

<?php
if($error) {
    echo(\"<p>$error</p>\");
} else {
    //**** process the form (ie mailto, stick it in a db etc *****
}
?>

Obviously, this is a really simple example. You can make it more complicated in various ways (for instance, I add all of the errors to an array with the key as the variable name - then I can highlight the problem fields!).

Andy

Megan posted this at 14:08 — 26th January 2007.

She has: 11,421 posts

Joined: Jun 1999

Okay, that's almost understandable! What does [incode]strlen[/incode] mean?

I think I might do some javascript for immediate feedback and then validate using php after the form is submitted.

Megan
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Megan posted this at 15:44 — 26th January 2007.

She has: 11,421 posts

Joined: Jun 1999

Another question: I'm using some javascript to show immediate feedback. How do I use event handlers without putting them into the HTML? So instead of:

<input type='text' size='30' name='name' id='name' value=""
 maxlength='255' onblur="validate('name');" />

I should have no onFocus in the link and have something like this in my javascript instead:

document.getElementById("name").onblur = validate('name');'

But that doesn't work at all. This is the best way to do it, right? I've seen people talk about avoiding event handlers in HTML but I can't find out how to make it work.

Megan
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andy206uk posted this at 16:42 — 26th January 2007.

He has: 1,758 posts

Joined: Jul 2002

In all honesty, I know very little about Javascript. I can't help you much with that.

strlen() returns the length of a string. If you ever want to know what a php function does just go to php.net/functionname and you'll get a nice description, examples of usage and lots of comments!

Andy