code: function waitelem (self, selector, done) {
    let elementPresent
    eval('elementPresent = function() {' + // eslint-disable-line
      `  var element = document.querySelector('${selector}');` +
      '  if (!element) { return null }' +
      '  for (let key in element) {' +
      '    if (key.startsWith(\'__reactInternalInstance$\')) {' +
      '      const compInternals = element[key]._currentElement;' +
      '      const compWrapper = compInternals._owner;' +
      '      const {props, state, context} = compWrapper._instance;' +
      '      return {props, state, context}' +
      '    }' +
      '  }' +
      '  return null;' +
      '}')
    waitfn.apply(this, [self, elementPresent, done])
  }
docs: Wait for a specified selector to exist.
  
  @param {Nightmare} self
  @param {String} selector
  @param {Function} done