query() helper function

query.js

const query = (selector, source = document) => {
  if (isElement(selector)) return selector

  if (typeof selector !== 'string') {
    throw new TypeError(`First argument must be a string. Instead got ${typeof selector}`)
  }
  if (!isElement(source)) {
    throw new TypeError(`Second argument must be a Node/NodeList. Instead got ${source}`)
  }

  const nodes = source.querySelectorAll(selector)
  return (nodes.length > 1) ? nodes : nodes[0]
}

// JavaScript Query Helper Function
///  alternative to document.querySelector() and document.querySelectorAll()
///  this coerces a selector into a Node/NodeList
///  returns a node if a single element matches the selector
///  returns a nodeList if multiple elements match the selector
///  a second argument allows a user to specify a source to query from