code: function indexInParent(element) {
    element = getElement(element);
  
    if (!element) return null;
  
    var i = void 0,
        current = void 0;
    for (i = 0, current = element; current = current.previousElementSibling; ++i) {}
  
    return i;
  }
docs: Returns index of element in parent's children.
  * @param {(string|Array|NodeList|HTMLCollection|NonDocumentTypeChildNode)} element - The element. Note that it'll be passed to getElement to ensure there's only one.
  @return {(number|null)} index - The position of element in his parent's children or null if no element found.
  @example //esnext
  import { createElement, append, indexInParent } from 'chirashi'
  const maki = createElement('.maki')
  append(document.body, maki)
  append(maki, ['.salmon[data-fish="salmon"]', '.cheese[data-cheese="cream"]']) //returns: <div class="maki"><div class="salmon" data-fish="salmon"></div><div class="cheese" data-cheese="cream"></div></div>
  indexInParent('.cheese') //returns: 1
  @example //es5
  var maki = Chirashi.createElement('.maki')
  Chirashi.append(document.body, maki)
  Chirashi.append(maki, ['.salmon[data-fish="salmon"]', '.cheese[data-cheese="cream"]']) //returns: <div class="maki"><div class="salmon" data-fish="salmon"></div><div class="cheese" data-cheese="cream"></div></div>
  Chirashi.indexInParent('.cheese') //returns: 1