proposal-pattern-matching VS proposal-decorators

Note, however, that there is a proposal to add pattern matching to JS.

There's an ECMAScript proposal that is in the works to add this feature to the language! It's going to look something like this.

More importantly, TypeScript typically commits to build things into itself when the proposal in JavaScript reaches Stage 3. The pattern matching proposal in JavaScript is Stage 1, but depends on many other proposals as well that may or may not need to be at Stage 3 as well for it to work. This particular proposal is interested on pattern matching on JavaScript Objects and other primitives, just like Python does with it’s native primitives. These are also dynamic types which helps in some areas, but makes it harder than others. Additionally, the JavaScript type annotations proposal needs to possibly account for this. So it’s going to be awhile. Like many years.

For true™ functional programming in JS, native pattern matching and partial function application are missing (at least for now: 1, 2). For proper OOP, it lacks real interfaces and compile-time dependency injection.

The proposal for pattern matching syntax seems more akin to what they're looking for.

https://github.com/tc39/proposal-pattern-matching

There's a proposal to add something like that to JavaScript but it's been stuck in limbo since 2017 although there are libraries like ts-pattern which implement it already.

I'll admit, it is easy to assert that the TypeScript language should not be involved in the matters of packages but I also wonder if we're moving towards a point where interfaces will be as common as namespaces and whether or not it would be sensible for the language to incorporate such type assertions into the language formally, after all, it already compiles to various forms of JavaScript and there is a stage 1 proposal submitted to the TC39 committee to give JavaScript pattern matching. If adopted, wouldn't it make sense to allow TypeScript to compile a type into a type guard for the native JavaScript pattern matcher?

Both are active tc39 proposals :)

https://github.com/tc39/proposal-pipeline-operator - Stage 2

https://github.com/tc39/proposal-pattern-matching - Stage 1

Hopefully we get both in the next couple of years.

We often add promising TC39 proposals into Civet so people can experiment without waiting.

We've added https://github.com/tc39/proposal-pipeline-operator, a variant of https://github.com/tc39/proposal-pattern-matching, a variant of https://github.com/tc39/proposal-string-dedent and others.

Since our goal is to be 99% compatible with ES we'll need to accommodate any proposals that become standard and pick up anything TC39 leaves on the table (rest parameters in any position, etc.)

Because many rules are common to many attributes (the coerceType operation is defined by WebIDL, or using similar rules, and the HTML specification defines a handful of microsyntaxes for the parseValue and stringifyValue operations), those could be packaged up in a helper library. And with decorators coming to ECMAScript (and already available in TypeScript), those could be greatly simplified:

Decorators are currently not a part of the standard JavaScript language. They are still being discussed in tc39 and have reached proposal stage 3. This means the spec has more or less stabilized and we can use them but they would be transplied before being run in the browser. This would be done via babel or tsc for most users

JavaScript was created a long time ago, and at the time of its inception, the authors decided not to use affirmative prefixes for boolean names. Now, they do their best by continuing to follow their convention, even if it goes against the community's opinion. Even if the authors wanted to introduce new naming conventions in the specification, they could not do it, at least not coherently. Old code cannot be renamed because JavaScript must remain backward-compatible. And starting to write new code using new approaches is not a great idea either, as there would be two ways to do the same thing, which is also undesirable.

2016-07 – Stage 2. After the decorators proposal reached stage 2, its API began to undergo significant changes. Furthermore, at one point the proposal was referred to as "ESnext class features for JavaScript." During its development, there were numerous ideas about how decorators could be structured. To get a comprehensive view of the entire history of changes, I recommend reviewing the commits in the proposal's repository. Here is an example of what the decorators API used to look like:

The example you've given isn't valid JavaScript, JS doesn't have decorators. (Although there is a stage 3 tc39 for it, afaik no browser has implemented it)

There was a decorators issue brought up in the meeting (issue 508) and decorators metadata, as noted in the article, is now at stage 3. So there's still active work being done on decorators. If I had to guess, I'd say they'd be a likely candidate for ES2024.

As per the proposal, decorators can be used with Classes and their elements such as fields, methods, and accessors. To leverage this feature, we need to ensure that our resolvers provider is an instance of a Class. Therefore, we will modify the code in src/api/users/users-resolvers.js to the following:

The modern version of decorators, which will be officially rolled out in TypeScript 5.0, no longer requires a compiler flag and follows the official ECMAScript Stage-3 proposal. Alongside a stable implementation that follows ECMAScript standards, decorators now work seamlessly with the TypeScript type system, enabling more enhanced functionality than the original version.

100% this. Going in depth of libraries will make you so much better developer than learning newest and coolest frameworks in JS ecosystem. Learn to create your own React, Promises, or anything you like in JS. It will give you immense perspective about these libraries. Once you start understanding them you will feel like they are not that complex and you can do it too. Go read TC39 proposals and issues people point out in them. You will see how JS is borrowing features from other languages.

The actual proposal gives the "@reactive" decorator as the first example, which just so happens is the only decorator that I use in my library with TypeScript's legacy decorator option. Was so happy to see they recognize this use case! https://github.com/tc39/proposal-decorators