a JavaScript library that allows you to use the HTML5 Forms chapters new field input types, attributes and constraint validation API in non-supporting browsers.
npm install h5fH5F 
===
The H5F script will detect if the browser has support for the HTML5 Forms Chapter and either hook into the native methods, attributes and events or emulate the new features in non-supporting browsers.
H5F offers support for most, but not all, of the HTML5 Forms Chapter:
* Input types: email and url
* Input attributes: pattern, placeholder, min, max, step, required
* Textarea attributes: placeholder and required
* Select attributes: required
* Form attributes: novalidate
* Submit attributes: formnovalidate
Also supported is the constraint validation API:
* Field validity object
* checkValidity() method on form or individual field
* setCustomValidity() method to set custom error message
* validationMessage attribute that returns the message set using setCustomValidity() method
``html
`
On page load you run the H5F setup method:
`js`
H5F.setup(document.getElementById("signup"));
For a working demo download the demo files.
#### Setting custom error message
With setCustomValidity() method you can set a custom error message on a field and it will be in an invalid state until the custom message is set back to an empty string.
`js`
document.getElementById("other").setCustomValidity("Please enter some information");
This field will be in a permanent invalid state, we can return the custom error message by using the validationMessage attribute
`js`
document.getElementById("other").validationMessage;
// "Please enter some information"
A good use case for this functionality is a password comparison field.
`js
var pass = document.getElementById("pass"),
cpass = document.getElementById("cpass");
if(cpass.value !== pass.value) {
cpass.setCustomValidity("Your password doesn't match");
} else {
cpass.setCustomValidity("");
}
`
#### Passing multiple forms
You can pass an HTMLFormElement, HTMLCollection of HTMLFormElements, or Array of HTMLFormElements.
`js`
H5F.setup([document.getElementById("form1"),document.getElementById("form2"),document.getElementById("form3")]);
#### Optional settings argument
The H5F.setup method also accepts a second optional argument so you can specify the fields validation class names:
`js`
H5F.setup(document.getElementById("signup"), {
validClass: "valid",
invalidClass: "invalid",
requiredClass: "required",
placeholderClass: "placeholder"
});
As well as form submit and invalid field event handlers, in case you need to hook custom functionality:
`js`
H5F.setup(document.getElementById("signup"), {
onSubmit: function (event) {},
onInvalid: function (invalidInputElement) {}
});
If you need to submit your form through AJAX, you must add your event handler using the onSubmit option, else, your handler will get called even if H5F invalidates the form. See A word on AJAX form submission under Form submission blocking.
onInvalid lets you add a callback for invalid fields to help you showing or doing special things when fields invalidate.
#### Form submission blocking
HTML5 forms will block form submission until the form is valid this can be switched off by setting the novalidate attribute on the parent form element.
`html
`
The above form regardless of attributes set won't validate and will submit, default behaviour is to block form submission.
You can also specify the formnovalidate attribute on a submittable element e.g. input or button. The attribute will bypass any form validation but only if the button with the formnovalidate attribute is clicked.
`html
`
##### A word on AJAX form submission
If you're going to submit your form through AJAX, you may be attaching a event handler to the form submit event. This handler will be called even if form is invalid for H5F. While we could avoid this using Event.prototype.stopImmediatePropagation() the reality is that older browsers don't implement it. So the workaround for this is that you add your event handlers using the provided onSubmit` setup option.
http://thecssninja.com/javascript/H5F