chirashijs/chirashi

import getElement from '../core/getElement'

/**
 * 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
 */
export default function indexInParent (element) {
  element = getElement(element)

  if (!element) return null

  let i, current
  for (i = 0, current = element; (current = current.previousElementSibling); ++i) {}

  return i
}