function isKeyable(value) {
  var type = typeof value;
  return (type == 'string' || type == 'number' || type == 'symbol' || type == 'boolean')
    ? (value !== '__proto__')
    : (value === null);
}
Checks if `value` is suitable for use as unique object key.

@private
@param {*} value The value to check.
@returns {boolean} Returns `true` if `value` is suitable, else `false`.