Publish a sub-directory in your repository as the contents of your gh-pages branch

ghpages.js

/**
  This script takes a sub-directory of your repository, renames relative links
  in HTML files to point to a Github Pages subdirectory, and publishes to your
  gh-pages branch.

  Use: 
    1. Download this script into the root of your project.
    2. Run npm install --save-dev fs-extra rebase gh-pages
    3. Rename "your-project" to the name of your Github project
    4. If you have more than one HTML file, add it to the "files"
    5. If your sub-directory is not "www", change "builddir"
    6. Run node ghpages.js
  
  You should now see that a gh-pages branch has been created/updated, and
  pushed to your remote!
*/
const ghpages = require('gh-pages');
const rebase = require('rebase');
const fs = require('fs-extra');

let subdir = 'your-project';
let builddir = 'www';

fs.removeSync(subdir);
fs.copySync(builddir, subdir);

// List all HTML files you use here.
let files = ['index.html'];
files.forEach((filename) => {
  let path = subdir + '/' + filename;
  let file = fs.readFileSync(path, 'utf8');
  let replacements = {
    '^\/(?!\/)': '/' + subdir + '/',
    '^(?!\/|http|https)': '/' + subdir + '/',
  };
  let rebased = rebase(file, {
    url: replacements,
    a: replacements,
    img: replacements,
    link: replacements,
    script: replacements
  });
  fs.writeFileSync(path, rebased);
});

ghpages.publish(subdir, function (err) {
  if (err) {
    console.log(err);
  }
});