Function push

packages/core/src/StateUtils.js:40–55

* Pushes a new route into the navigation state. * Note that this moves the index to the position to where the last route in the * stack is at.

(state, route)

   * stack is at.
   */
  push(state, route) {
    invariant(
      StateUtils.indexOf(state, route.key) === -1,
      'should not push route with duplicated key %s',
      route.key
    );

    const routes = state.routes.slice();
    routes.push(route);

    return {
      ...state,
      index: routes.length - 1,
      routes,
    };
  },

  /**
   * Pops out a route from the navigation state.