app-start.md

Custom Application Startup

When the application starts up, we often need to set up some initialization logic. The application bootstraps with those specific configurations. It is in a healthy state and be able to take external service requests after those configurations successfully applied. Otherwise, it failed.

The framework starts with a file called app.js that executes the application initialization logic, if present, and it returns a function.

For example, we need to load a list of national cities from the remote server during application startup for subsequent use in the controller:

// app.js
module.exports = app => {
  app.beforeStart(async () => {
    // The lifecycle method runs before the application bootstraps
    app.cities = await app.curl('http://example.com/city.json', {
      method: 'GET',
      dataType: 'json',
    });
  });
};

cities attribute has attached on the global app. It can be accessed in the controller,

// app/controller/home.js
class HomeController extends Controller {
  async index() {
    // now you can use `ctx.app.cities`
  }
}

Note: When the framework executes the lifecycle method beforeStart, do not run time-consuming operation. The framework enables a Timeout setting by default when it starts up.