npm install w3cjs

var w3cjs = require('w3cjs');

var results = w3cjs.validate({
    file: 'demo.html', // file can either be a local file or a remote file
    //file: 'http://html5boilerplate.com/',
    output: 'json', // Defaults to 'json', other option includes html
    callback: function (res) {
        console.log(res);
        // depending on the output type, res will either be a json object or a html string
    }
});

var w3cjs = require('w3cjs');
describe('html validation', function(){
  it('index page should have no html errors', function(done){
    w3cjs.validate({
        file: 'index.html',
        callback: function (res) {
                console.log(res);
            if (res.messages.length > 0 ) {
                throw {error: 'html errors have been found', results: res};
            };
            done();
        }
    })
  })
})