a way to check validity of HTML5 forms?

Solution 1:

there are two ways to check the validity.

1. inputElement.checkValidity() returns true or false
2. inputElement.validity returns the validity-state object. inputElement.validity.valid returns true/false

Instead of using keyup, you can also use the 'input' event. All browser, which have implemented the constraint validation API, have also implemented the input-event.

If you are using option 1 above, Opera has a bug here and will show its validation hint. So you should use 2.

I have created a html5 forms library, which implements all unknown features to incapable browsers + fixes issues in HTML5 browsers. So everything works like defined in the spec, but it's built on top of jQuery. (http://afarkas.github.com/webshim/demos/index.html).

Solution 2:

You can use the pattern attribute.

It will validate it client side, so no need to validate it again client side.

jsFiddle.

But, make sure you do it again server side.

Also note, because browser compatibility is quite poor right now, JavaScript is the norm for validating client side.

Solution 3:

To complement, you can check each element was invalid and, for example, set a focus in the first invalid element, by this code:

var Form = document.getElementById('FormID');
if (Form.checkValidity() == false) {
    var list = Form.querySelectorAll(':invalid');
    for (var item of list) {
        item.focus();
    }
}