HTML5 has a built-in validation that doesn't require any JavaScript. However, currently, it only works in Webkit browsers and can't be used in Firefox, Opera or IE.

jQuery.Html5form is a jQuery plugin that adds the lacking HTML5 form validation features to non-compatible browsers.

jQuery HTML5 Form

It doesn't require any custom functions or coding. Just create your form with the HTML5 syntax and it'll execute them automatically.

Optionally, the plugin offers features to help customizing how the errors will be handled like the the error messages, where they'll be displayed, their styles, etc.

And, it works with multiple forms on the same page as well (each of them can be customized differently).

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