Question

as you might know, within the HTML5 spec we got some new attributes for <input> elements, such as required and pattern. This provides as a great way of validating user-input and we can even visualize it using CSS and pseudo selectors. Example

HTML

<input type="number" pattern="\d+" required/>

CSS

input:required:valid {
    border: 1px solid green;
}

input:required:invalid {
    border: 1px solid red;
}

If that <input> element would be part of an <form> element, an user wouldn’t be able to submit that in invalid state.

However, my question is, what if we want to use those new attributes without <form> elements ? Is there a way to access the current state of such an <input> node through ECMAscript directly ?

Any event ? Any listener ?

Answer 1

As pointed out by @Zirak, there is the checkValidity method, part of the Constraint Validation API.

var s = document.createElement('input');
s.checkValidity(); // true
s.required = true;
s.checkValidity(); // false

However, checkValidity fires an invalid event if it’s invalid. (The form will be red-outlined.) You may want to use the willValidate property (or the .validity.valid property) instead.

Also, the validity property is quite interesting to watch (more information about what each property means on the Constraint Validation API):

s.validity
    ValidityState
        customError: false
        patternMismatch: false
        rangeOverflow: false
        rangeUnderflow: false
        stepMismatch: false
        tooLong: false
        typeMismatch: false
        valid: false
        valueMissing: true

This article points out the differences in implementations between the browsers: http://www.html5rocks.com/en/tutorials/forms/constraintvalidation/ (i.e: it’s a mess, as usual.)

You can also listen to the invalid event, triggered on submit of the form, or when the checkValidity method is called.

Demo: http://jsfiddle.net/XfV4z/