How to use:

const sel = require('selector-from-element')

var input = document.createElement('input')
input.name = "password"
let form = document.querySelector('body > form#super-form')
form.appendChild(input)

let selector = sel(input)
selector === '#super-form input[name="password"]'

Full code for this package:

function selectorFromNode (node) {
  if (node.id) {
    return '#' + node.id
  }

  let tag = node.tagName.toLowerCase()

  var special = ''
  if (node.name) {
    special += `[name="${node.name}"]`
  }

  var cls = ''
  if (!special && node.className) {
    cls = node.className.split(/ +/g)
      .map(cls => '.' + cls)
      .join('')
  }

  var pos = ''
  if (!special) {
    var nthoftype = 0
    for (let i = 0; i < node.parentNode.children.length; i++) {
      let child = node.parentNode.children[i]
      if (child.tagName === node.tagName) {
        nthoftype++
      }
      if (node === child) {
        pos = `:nth-of-type(${nthoftype})`
        break
      }
    }
  }

  let sel = tag + special + cls + pos
  if (node.parentNode === document.body) {
    return 'body > ' + sel
  } else {
    return `${selectorFromNode(node.parentNode)} > ${sel}`
  }
}