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LoopBack 4 August 2020 Milestone Update

· 5 min read
Janny Hou

Originally published on

Our focus in August is the documentation restructure. The layout of several main sections are reorganized for easier navigation. Another significant improvement is about the request handling. More flexible approaches of adding LoopBack style middleware and express middleware are introduced in @loopback/rest.

We would like to appreciate Agnes Lin's great contributions during her internship. There has been so much fun and pleasure working with her! She will be continue helping us part time. Good luck with your school.

Keep reading to learn about the improved documentation and recently added features!

Documentation Enhancements

Reorganizing the Concepts List

The fundamental concepts were listed in section "Behind the Scene" sorted by the publish date. To have a concise name and a more organized layout for users to search, we renamed the section to be "Concepts" and restructured the documentations into the following sub-sections:

  • Crafting LoopBack 4
  • Core
  • Data Access

You can visit the more organized contents in

Reorganizing How-to Guide List

The "How-to Guide" is also reorganized by topics. The existing tutorials are classified into the following sections for users to search quickly:

  • Building REST APIs
  • Creating Other Forms of APIS
  • Accessing Databases
  • Accessing Services
  • Validating Data
  • Securing Applications
  • Deploying Applications
  • Troubleshooting

You can visit the more organized contents in

Adding Property Types

We added documentation for LoopBack 4 types including the syntax of model property definition in page

Adding Application Layout

We added project layout for LoopBack 4 applications in page, users can find each file's meaning and responsibility in the application scaffolded by lb4 app.

Cleaning up Extensions

We are seeing more users creating extensions and it's a good time to make the extension creation experience easier and smoother. Therefore the extension generator and related documentations are updated to align with the latest code base. You can check the latest material in:

And run lb4 extension to create extensions with the new component template.

Renaming Legacy Juggler

The term "legacy juggler bridge" might give the wrong impression to users that the loopback-datasource-juggler won't be supported or not working well because of the "legacy" word. So we removed the misleading word "legacy" across the documentations and CLI prompts.

loopback-datasource-juggler is still well maintained and we have a plan to modernize it. Feel free to join the discussion in issue #5956 if you are interested.


Restructuring Connector Reference

The current connector contents are mixed with how-to guides, references and tutorials. The spike story 5961 came up with a better plan to reorganize them into the four quadrants layout:

  • Connector concepts, its role in the framework and its relations to other artifacts will go to section "Concepts/Datasources".
  • Datasource level configurations and features like migration/discovery will go to section "How-to Guides/Configuring DataSource".
  • All the other connector specific tutorials will go to section "Tutorials/Connect to back-end tutorial".

Improving REST Experience

REST Middleware

A big feature took place in @loopback/rest to support more flexible ways to add express middleware for handling requests. PR #5366 added a middleware based sequence and wrapped existing actions as middleware. The new usage is documented in the following pages:

Optimizing Middleware Based Sequence

PR #6062 optimized middleware based sequence and its middleware providers to be singletons:

  • MiddlewareSequence is now a singleton and it caches a list of middleware.
  • Built-in middleware providers are now singletons.
  • Validating sorted middleware groups is supported. Error will be reported if a middleware is unreachable.

Improving Serviceability of @loopback/rest

There are several improvements made for easier debugging and error tracing in @loopback/rest module:

  • PR #6159 added more debug information for request parsing, routing, and method invocation. The debugging keywords are loopback:rest:find-route, loopback:rest:invoke-method, and loopback:rest:parse-param.

  • The route description is improved in PR #6188 to include the verb and the path.

  • PR #6171 added HTTP server options and status information in the debug string. The debugging keyword is loopback:http-server.

Switching to DCO

To make your contribution process simpler, we have changed the contribution method from CLA to DCO for loopback-next and most of the connector repositories. Be sure to sign off your commits using the -s flag or adding Signed-off-By: Name<Email> in the commit message. For more details, see


  • PR #6172 makes sure the REST options are passed to http-server.

  • PR #6105 Reworked the validation code to use exiting RestHttpErrors.invalidData error. This way the error object includes the parameter name in the error message & properties and has a machine-readable code property.

Community Contributions

Thank you for the contribution coming from the community. Here are some of the contributions that we'd like highlight:

  • Thanks to Nico Flaig's contribution! Now @loopback/authenticate supports applying multiple authentication strategies to one endpoint. The new syntax of decorator is:

    strategyOne | strategyOneWithOptions,
    strategyTwo | strategyTwoWithOptions
    myFunction() {}

    The new syntax is well documented in page Authentication Decorator.

  • We appreciate Madaky's feature PR #5589 which adds the token refresh service in extension @loopback/authentication-jwt. You can check the new guide to try it.

  • Many thanks to Rifa Achrinza's contribution in PR 6153. The order filter now supports string value as the shortcut in addition to the existing array value. You can specify an order filter as {order: 'name DESC'}.

Enriching LoopBack and its Community - You are Invited!

As mentioned in our recent blog post, your contribution is important to make LoopBack a sustainable open source project.

Here is what you can do:

Let's make LoopBack a better framework together!