Function router

packages/dva/src/index.js:36–42

(router)

  return app;

  function router(router) {
    invariant(
      isFunction(router),
      `[app.router] router should be function, but got ${typeof router}`,
    );
    app._router = router;
  }

  function start(container) {
    // 允许 container 是字符串，然后用 querySelector 找元素