selector.js

const rx = {
  id: /^#([\w\-]+)$/,
  className: /^\.([\w\-]+)$/,
  tagName: /^[\w\-]+$/,
  name: /^\[name=["']?([\w\-]+)["']?\]$/
};

function $(selector, context) {
  let result;
  let m;
  if(!context || !context.querySelector) {
    context = document;
  }
  if (m = rx.id.exec(selector)) {
    let element = document.getElementById(m[1]);
    result = element ? [element] : [];
  } else if (m = rx.className.exec(selector)) {
    result = context.getElementsByClassName(m[1]);
  } else if (m = rx.tagName.exec(selector)) {
    result = context.getElementsByTagName(m[1]);
  } else if (m = rx.name.exec(selector)) {
    result = context.getElementsByName(m[1]);
  } else {
    result = context.querySelectorAll(selector);
  }
  return Array.of(result);
};