WIP: ES2015 heredoc helper

heredoc.js

function chainOptions(props, fn) {
  function getWrapper(options = {}) {
    const wrapper = (...args) => fn(options, ...args);
    props.forEach(prop => {
      Object.defineProperty(wrapper, prop, {
        enumerable: true,
        get() {
          return getWrapper(Object.assign({}, options, {[prop]: !options[prop]}));
        },
        set() {},
      });
      wrapper[prop] = (...args) => wrapper(...args);
    });
    return wrapper;
  }
  return getWrapper();
}

function templateTagDefault(strings, ...values) {
  return strings.reduce((result, string, n) => result + (n > 0 ? values[n - 1] : '') + string, '');
}

const heredoc = chainOptions(['trim', 'unindent', 'oneline'], function({trim, unindent, oneline}, ...args) {
  let s = templateTagDefault(...args);
  let lines = s.split('\n');
  if (unindent) {
    // Convert any only-whitespace lines to ''
    lines = lines.map(s => /\S/.test(s) ? s : '');
    // Unindent every line by the minimum indent shared by all non-whitespace lines.
    const indent = lines.filter(Boolean).reduce(
      (n, s) => Math.min(n, s.match(/^\s*/)[0].length), Infinity);
    lines = lines.map(s => s.slice(indent));
    // Remove any leading/trailing whitespace lines.
    s = lines.join('\n');
    if (trim) {
      s = s.replace(/^\n+|\n+$/g, '');
    }
  }
  else if (oneline) {
    if (trim) {
      lines = lines.map(s => s.replace(/^\s+|\s+$/g, '\uFFFF'));
      s = lines.join('\uFFFF');
      s = s.replace(/\uFFFF+/g, ' ').replace(/^\s+|\s+$/g, '');
    }
    else {
      s = s.replace(/\n+/g, '');
    }
  }
  else if (trim) {
    s = s.replace(/^\s+|\s+$/g, '');
  }
  return s;
});

output.txt

Before text.
  array has length=3 and items=a-b-c

  test
    1 2 3

After text.

usage.js

const a = ["a", "b", "c"];
const foo = heredoc.unindent.trim`
  
                          

  
  Before text.
    array has length=${a.length} and items=${a.join("-")}
    
    test
      1 2 3

  After text.
  
             
  
`;

Done. https://github.com/cowboy/node-heredoc-tag