docs: function printWarning(format, ...args) {
    var argIndex = 0;
    var message = 'Warning: ' + format.replace(/%s/g, () => args[argIndex++]);
    if (typeof console !== 'undefined') {
      console.error(message);
    }
    try {
      // --- Welcome to debugging React ---
      // This error was thrown as a convenience so that you can use this stack
      // to find the callsite that caused this warning to fire.
      throw new Error(message);
    } catch (x) {}
  }