phpjs/experimental/xdiff/xdiff_file_diff.js

php.js offers community built php functions in javascript

function xdiff_file_diff(old_file, new_file, dest, context, minimal) {
  // http://kevin.vanzonneveld.net
  // +   original by: Brett Zamir (http://brett-zamir.me)
  // % note 1: Depends on file_put_contents which is not yet implemented
  // -    depends on: xdiff_string_diff
  // -    depends on: file_get_contents
  // -    depends on: file_put_contents

  old_file = this.file_get_contents(old_file);
  new_file = this.file_get_contents(new_file);
  return this.file_put_contents(dest, this.xdiff_string_diff(old_file, new_file, context));
}