lodash/_isKey.js

define(['./isArray', './isSymbol'], function(isArray, isSymbol) {

  /** Used to match property names within property paths. */
  var reIsDeepProp = /\.|\[(?:[^[\]]*|(["'])(?:(?!\1)[^\\]|\\.)*?\1)\]/,
      reIsPlainProp = /^\w*$/;

  /**
   * Checks if `value` is a property name and not a property path.
   *
   * @private
   * @param {*} value The value to check.
   * @param {Object} [object] The object to query keys on.
   * @returns {boolean} Returns `true` if `value` is a property name, else `false`.
   */
  function isKey(value, object) {
    var type = typeof value;
    if (type == 'number' || type == 'symbol') {
      return true;
    }
    return !isArray(value) &&
      (isSymbol(value) || reIsPlainProp.test(value) || !reIsDeepProp.test(value) ||
        (object != null && value in Object(object)));
  }

  return isKey;
});