RFC: TypeScript / es6 / es7

[ritch]

I think the main goal of loopback-next should be TypeScript and es6-7 as first class features. Below are the goals:

1. rewrite LoopBack source code as TypeScript classes using es6 / 7 features best practices
2. use TypeScript native modules eg. import and export.
3. promises first and everywhere
4. async and await everywhere

Below is brief list of impact for discussion.

1. drop callback API ??? - we need to focus on promise support, can we do that without dropping callbacks?
2. remove all uses of require()
3. change model script syntax - now export es6 class ???
4. shouldn't force users to use TypeScript - need to provide docs as both TypeScript and JavaScript
5. would tests need to be rewritten in TypeScript ???
6. drop custom impl of mixin and class in juggler

Anything else?

@bajtos @raymondfeng @superkhau

[bajtos]

I think the main goal of loopback-next should be TypeScript and es6-7 as first class features.

@ritch could you please add arguments supporting this statement? What are the benefits we would like to get from using TypeScript in our code base? What are the costs we have to pay?

While I personally like TypeScript and I think we should make it easy to write loopback applications in TypeScript, at the same time I am not convinced that the loopback core has to be written in TypeScript too.

Here are my concerns:

(1) In Node.js ecosystem, the convention is to use vanilla javascript with no transpilation. This has two aspects:

• People may be reluctant to use a framework/module that's written in a transpiled language like TypeScript, i.e. we may loose a (big?) part of our user base.
• We will make it more difficult for people to contribute changes, because people familiar with ES6 only will have to learn TypeScript.

Anyone remember the time 2-3 years ago, when CoffeeScript was the most popular transpiled language? Many people (including myself) were looking down on packages written in CoffeeScript, and contributing patches was definitely a pain.

Do we want LoopBack to become that kind of project?

I know that Angular2 is using TypeScript everywhere. Their situation is different though, because virtually everybody is transpiling their browser scripts these days. Node.js land is different AFAIK.

(2) There are other competing type checkers, most notably https://flowtype.org/. To my knowledge, there is no clear winner in this space yet. Do we want to put our bets on a solution that may become obsolete in the near future?

(3) Performance and usability penalties.

• async/await is not available natively in any Node.js version yet, 7.x provides async/await behind a feature flag. Transpilers have to either convert the code to vanilla ES5, or use generators introduced by ES6 - I don't know which approach TypeScript is taking. I am pretty sure that generators were not optimized much in V8 yet. My point is that async/await is almost certainly introducing non-negligible performance penalty. Are we ok with that?
• The performance of built-in Promises is not on par with callbacks yet AFAIK. (Bluebird claims it's at least as fast as callbacks, can we use it with TypeScript?)
• Promises (at least the built-in V8 Promise) don't play well with post-mortem debugging in Node.js (e.g. node --abort-on-uncaught-exception will report incorrect stack trace in the core dump file produced).

(4) ES6 modules in Node.js are not stable yet. Things may change and we may be forced to update our codebase to accommodate for that. Is the new import/export syntax worth this cost?

In fact, it looks the module loader specification is not complete yet, see https://whatwg.github.io/loader/ (via nodejs/help#53):

Status

This document is a work in progress and dreams of becoming a living standard.

Further reading:

• https://nodesource.com/blog/es-modules-and-node-js-hard-choices/
• In defense of .js
• Understanding the hard choice

---

I would prefer to start with a discussion of what benefits we would like to get from new language features available in post-ES5 world (focus on "why" we want to make the change, now "how"/"what").

[bajtos]

rewrite LoopBack source code as TypeScript classes using es6 / 7 features best practices

IMO, there are two steps available here:

1. Start using ES6 class keyword
2. Start using TypeScript and add additional type information to our classes

If our primary motivation is to start using the class keyword (which is just a syntactic sugar, BTW), then I think we don't need TypeScript for that.

I personally find the class keyword/concept useful and use it in new code. However, I think the benefits of class are not worth the cost of rewriting all our code to use class.

use TypeScript native modules eg. import and export.

See my point above. I think import/export has very little benefits compared to current require(), and considering that the spec is not final yet, I'd prefer to avoid using it.

promises first and everywhere

+1, even though it may cause more difficult post-mortem debugging

TBH, I think this is a change that can be implemented incrementally in the current code base, no need for a big rewrite.

drop callback API ??? - we need to focus on promise support, can we do that without dropping callbacks?

Promise-based APIs can be relatively easily amended to support callbacks, see e.g. Bluebird's .asCallback() API

I am personally fine to move on and drop callbacks entirely.

async and await everywhere

See my comment above, I think async/await is not ready for prime time/production yet.

remove all uses of require()

See my comment above, I think this does not have any significant benefits and is not worth the costs.

change model script syntax - now export es6 class ???

Yes please, this would be awesome! I also think it may not be possible implementation-wise if we want juggler to auto-generate stuff using JSON config, further research is needed IMO.

In fact, I think this is the most important benefit we can offer LoopBack users in loopback-next - the ability to write their models/controllers/etc. using the class keyword in ES6 or using fully-typed TypeScript classes.

However, I am not convinced that switching to TypeScript is necessary in order to get there.

[raymondfeng]

We should also separate the following concerns:

• Rewrite LoopBack code base with TypeScript
• Allow application/extension logic to be written in TypeScript in addition to Plain JS

[raymondfeng]

My take on TypeScript adoption:

Pros:

• Productivity gain for LoopBack developers (optional type/interface checks, code refactoring, static verification, tooling)
• State of the art JavaScript (async/await, decorators, ...)
• More attractive to developers from Java/C# background

Cons:

• Transpilation needed
• Learning curve of another new language
• Add complexity to support both TypeScript and Vanilla JS for extension/application logic

I'm open to trying it out with a few modules.

[superkhau]

I agree with everything @bajtos + @raymondfeng said above. I still don't see the major reason for jumping to typescript in nodeland.

Pros:

• Biggest selling points what @raymondfeng mentioned above

Cons:

• Unattractive to an (unknown ATM) portion of node users (how do we finalize on the language without knowing the popularity/usage numbers etc)
• Transpilation languages like CoffeeScript haven't stuck in JS land period (ie. CoffeeScript like @bajtos mentioned above)
• Need to add a build system to complicate things (gulp vs plain npm scripts) -- I did get some suggestions from a community member on gitter though regarding https://github.com/TypeStrong/ts-node which would alleviate dev time issues, but IMO it's still more complication in the mix)
• I don't want to run into Angular 2/React situation where we force typescript down community's throats and narrow down our contributor market (ie. 100% node now to only TS contributors)

IMO, all this extra complication is not needed. I believe everyone using LoopBack wants to see feautres and extensibility for features we don't currently support OOB. TS may make us better (or worse), but that is not what is going to sell LB4. Supporting both TS + vanilla JS IMO is doubling our effort for what I'm going to say little gain.

Anyways, it all comes down to who we're selling to. Are we targeting only Java/C# background devs at the expense of vanilla JS devs?

Personally, I am quite interested in giving it a shot (new shiny toy syndrome). Just not sure about the long term ramifications for the LB project itself.

[ritch]

Skate to where the puck is going, not to where it is.
-Gretzky

There is something entirely missing from this thread... We are discussing the current state of affairs in node / javascript land. Remember and always consider this quote in the design of loopback-next. The release time frame we are talking about is ~ 6 months (much longer than the original release of LB btw, and about the timeframe of LB 2). How much can change in 6 months? Node.js went from a project that no one cared about to millions of users in that time frame.

A lot of the points above are arguments against things that no one is advocating for. Yes the class keyword is syntactic sugar for:

function Foo() { 
}
Foo.prototype.bar  = function() { 
}

(btw this is the first code in this thread about code... another thing to keep in mind)

My point is: syntax is not the focus here.

TypeScript - JavaScript that scales.

The idea is to embrace the ideals of TypeScript. Take this snippet from an email I just received from one of our customers:

Currently we have ~100 people developing product code with Node, Loopback, Express, Passport etc. By September that number will be close to 250.

Our customers need a framework that scales to dozens and even hundreds of developers. Its the reason TypeScript exists and is gaining traction. It is so much more than the class keyword.

Tooling

TypeScript users share the same IDE: Visual Studio code. This means that the LoopBack ecosystem could someday be filled with useful best practices around that IDE and even plugins that improve the dev experience. Right now that effort is split between various editors and basically non-existent.

Static analysis also makes more robust tooling possible. Its the foundation which this scalability comes from. The ability to easily refactor code without the common human introduced errors. Dev and Compile time checking. Think about the effort we have spent on liniting, Our users have this same problem but don't have the same expertise and time we do to setup complex linting solutions (eg. 1 linting config that works across many projects).

Best Practices

Large scale development teams are usually led by folks who understand traditional OO best practices. We might all agree that OO should die in favor of functional programming, but I don't think thats going to happen very soon (although I wish it would). LoopBack already has psuedo OO design baked into is DNA (see example below)

// JavaScript - now
var MyModel = loopback.Model.extend('MyModel', properties, options);

// TypeScript
class MyModel extends Model { // this removes a lot of ugly code in Juggler

Anyways there is plenty to discuss... and the discussion could go on forever. My plea is that we get deeper into the actual code so the conversation is less abstract. That way we can comment on our experience with type script, whether thats performance, cost vs benefit, etc.

[ritch]

Closing this for now. Lets revisit after the spike.

[bajtos]

// TypeScript
class MyModel extends Model { // this removes a lot of ugly code in Juggler

FWIW, this means that in order to create a custom MyModel, we must have access to the base Model class. The ways how to achieve that, which I am aware of, look too complex to me:

• All components used by the application are depending on the very same loopback version (this is highly improbable).
• Components need dependency injection allowing the application to provide them with the base Model class to use. This makes the example less simple and may break static code analysis/code completion:
  module.exports = (Model) => class MyModel extends Model {
  In fact, the type system may not even support a construct like this - how are we going to express that the exported method returns a type that's created inside the method and does not exist before the method is called? We also cannot provide type information for the Model argument, because the type depends on the application calling this code. (There may be other options for dependency injection in TypeScript though.)
• Each component brings its own version of loopback. Both the framework and the applications must be prepared to handle this.

I was thinking quite a bit about this problem in the past, the solution I proposed for controllers (see https://github.com/strongloop-internal/scrum-loopback/issues/614#issuecomment-187124065) is to reverse the inheritance hierarchy:

// in a component or an app
class MyModel { // no dependency on anything from LoopBack yet
 // ...
}

// in LoopBack
app.model = function<Model>(ctor: Model, options: ModelOptions) {
  // build a subclass of ModelCtor that adds data-access methods like Model.create
}

This way, the components do not depend on LoopBack to implement their custom behaviour (business logic) and the dependency-versioning issue I described above is no longer relevant.

Of course, I don't whether TypeScript/ES6 classes are powerful enough to allow this construct. We may need to investigate different approaches as part of the spike.

The goal of my comment is to raise awareness of this problem.

---

One more thing to verify as part of the spike: are static methods inherited in ES6/TypeScript classes? In the current design, most data-access methods are static, i.e. MyModel.create, and inherited from base PersistedModel.

[bajtos]

@ritch I think we all agree that users should be able to write their applications in TypeScript. The part where we do not agree is whether the framework itself must be written in TypeScript too.

Let's wait for the outcome of the spike to discuss this topic more.

[ebarault]

Hi, thanks for letting me join your discussions regarding LoopBack next with an early-preview ticket 👍

Given my experience of the framework as a contributing user for 2 years, and a community maintainer for 2 months. I don't see how you will humanly be able to carry on the support on LoopBack 2/3 in vanilla js and the development of LoopBack 4 in ts with sufficient velocity.

Why this total rebuild? IMO time would be more profitably invested on existing code reassessment to consolidate the existing features. Take for example what i'm trying to achieve with polymorphic relations and model inheritance.

I'm afraid that during this redesign more bugs will be added on top of existing ones and it will soon become unmanageable to identify the origins of the problems. On some features already I need to dig in 4 years of commit history to understand the stacking of logics contributing to a same feature.

Also, i take from other discussions in this repo that you wish to scale up through more community involvement which is great, but there's a huge risk of fragmenting the community here, not only because of the choice of this or that coding language, but because people have invested time to understand how the framework is built (including its subtleties) and how to contribute to it: I'd kindly suggest to move the framework step by step to keep active contributors on board. Progressive support for es6 class could be brought the same way promises were introduced in LB.

Remember these active contributors are also the same that use LoopBack every day to build applications with it and that will stay with LB3 for a while. Going with ts is like asking them to support bug-fixing and evolutions on both the vanilla js version and the new ts version. Huh huh...

Support for applications leveraging ts is a different story.

[bajtos]

Thank you @ebarault for a thoughtful comment. Frankly, I don't know what to say - this decision was made mostly by @ritch despite my/our objections, see his #6 (comment)

Progressive support for es6 class could be brought the same way promises were introduced in LB.

I think adding support for ES6 classes to the current design of model/model-builder/model-registry is much more difficult than may look at the first sight. Right now, the model constructor is generated by model-builder and registered in model-registry. I think we would need to significantly change this part to support ES6 class inheritance, which may in turn break a lot of things across the codebase.

I am not saying it's not doable, it's just one of the pain points where a clean rewrite looks like an easier path than trying fix the existing codebase.