function jsxDEV(type, config, maybeKey, source, self) {
  {
    var propName; // Reserved names are extracted

    var props = {};
    var key = null;
    var ref = null; // Currently, key can be spread in as a prop. This causes a potential
    // issue if key is also explicitly declared (ie. <div {...props} key="Hi" />
    // or <div key="Hi" {...props} /> ). We want to deprecate key spread,
    // but as an intermediary step, we will use jsxDEV for everything except
    // <div {...props} key="Hi" />, because we aren't currently able to tell if
    // key is explicitly declared to be undefined or not.

    if (maybeKey !== undefined) {
      key = '' + maybeKey;
    }

    if (hasValidKey(config)) {
      key = '' + config.key;
    }

    if (hasValidRef(config)) {
      ref = config.ref;
    } // Remaining properties are added to a new props object


    for (propName in config) {
      if (hasOwnProperty.call(config, propName) && !RESERVED_PROPS.hasOwnProperty(propName)) {
        props[propName] = config[propName];
      }
    } // Resolve default props


    if (type && type.defaultProps) {
      var defaultProps = type.defaultProps;

      for (propName in defaultProps) {
        if (props[propName] === undefined) {
          props[propName] = defaultProps[propName];
        }
      }
    }

    if (key || ref) {
      var displayName = typeof type === 'function' ? type.displayName || type.name || 'Unknown' : type;

      if (key) {
        defineKeyPropWarningGetter(props, displayName);
      }

      if (ref) {
        defineRefPropWarningGetter(props, displayName);
      }
    }

    return ReactElement(type, key, ref, self, source, ReactCurrentOwner.current, props);
  }
}
https://github.com/reactjs/rfcs/pull/107
@param {*} type
@param {object} props
@param {string} key