Checks if HTML is valid to W3C standards using the W3C Validation Service

(sudo) npm i -D posthtml-w3c

For general usage and build process integration see PostHTML Docs

You can modify the behavior by passing an options object to the method:

var options = {
  filter: [
    'An “img” element must have an “alt” attribute, except under certain conditions.',
  ],
  hideEmpty: true
}
var validate = require('posthtml-w3c')(options)

• filter - an array of strings to filter the messages. If you want to silence some warnings or errors, you can add a substring of the message to this collection. Any messages that contain a string from the filter array will be ignored.
• hideEmpty - if true and no messages are found, nothing will be printed. If false or skipped and no messages are found, the header and summary will be printed. This option is backward-compatible.

const fs = require('fs')
var posthtml = require('posthtml')
var validate = require('posthtml-w3c')()
var html = fs.readFileSync('./index.html', 'utf8')
posthtml([ validate ])
  .process(html)
  .then(result => console.log(result.html))

PostHTML W3C Validation
-----------------------
⚠ info [14:5]
Consider using the “h1” element as a top-level heading only
(all “h1” elements are treated as top-level headings by many
screen readers and other tools).
⚠ info [19:5]
Consider using the “h1” element as a top-level heading only
(all “h1” elements are treated as top-level headings by many
screen readers and other tools).
⚠ info [18:5]
Consider using the “h1” element as a top-level heading only
(all “h1” elements are treated as top-level headings by many
screen readers and other tools).
⚠  3 Errors