Actually, class object's context is mutable.

Base classes don't really return anything (other than hosting properties and funtions) rather, they morph all things public to be a part of the parent. My point is that anyone reading my code (including myself) can open the file and see the overview of the file, then quickly jump to the relevant function using standard IDE tools. How to write an ES6 class React Component that extends a functional component? JS Class is arguable. I'll have to take some time to read through it and consider it. Add "noStrictGenericChecks": true in tsconfig.json file under "compilerOptions" node as shown in below image & build application. You can, of course, use a getter and a setter for each public property to make them accessible while keeping the closure and its advantages, but at that point the complexity of the code really ramps up while the readability falls, and personally, I just don't know if it's worth the trade-off: That up there feels like a lot of boilerplate to produce an object with three properties, just so I can occasionally write = myDoggo.speak instead of = () => myDoggo.speak().

You will find the context being mutable, and will be forced to bind them everywhere. I am not going to pretend to be the know-it-all :), So we pretty much have the same background :).

As a substitute, enforce type correctness in the business logic, detached from the resource facing layer. @Alan, thanks for the in-depth response! Just put in checks when used.

Unless what you meant was that classes as a paradigm are syntactic sugar that add unnecessary complexity, regardless of the language in question, in which case I have to disagree even more strongly, though that's a much longer conversation. Is there an accepted paradigmatic solution here? Not checking the types in libraries with flag --skipLibCheck set to true. Change the string or string[] returns to type of any. I think my biggest complaint about JS classes is the encapsulation. I just uninstalled this from Control panel and it works for me as Visual Studio 2017 already has this.

Others may feel differently, but it's how my brain works. Compilers in certain languages are proven to save time and improve quality (C/C++ for example) and by definition it serves the sole purpose of syntactic sugar. Thanks Ken for the elegant explanation of why some of us prefer the Class construct. TypeScript 2.4 has a strictness change, and Subject isn't lifting to the correct Observable. I guess enforcing strict TypeScript in the ObjectionJS is not the best angle to approach this problem.

Now of course, one way to solve this problem is to use purely private vars and closures like you did in your Animal example, but personally, I have one really big problem with that approach: it makes the properties themselves inaccessible. That is exactly my point. So the behavior you've shown would be expected because mockElement.onClick is not a Person object. With you every step of your journey. Out of interest, do you use an ORM with TS? With the way of packaging nowadays, there is not much practical you cannot do without classes.

Start your own website to earn without any coding, Click to share on Facebook (Opens in new window), Click to share on Twitter (Opens in new window), Best Datepicker for Angular 4/5/6 with Bootstrap projects, Angular 8 Loading / Spinner ng-spin-kit component Example . Also, check this out, TypeScript 3.5's feature higher-order type inference which is super neat. This is because you neither return a value, nor do you have an explicit type on that getter. is a bit more useful.

As I mentioned, very little difference either way. function handleRelations(modelClass: T) {. Hoisting is a step in the interpretation of a JavScript scope wherein all declarations are basically plucked out of their place in the script and moved to the top of the scope. To understand this more specifically, if someone write some piece of code that accepts objects of type Model based on the above class in the article, f.e.

However, the benefit here is that you can adopt infinite number of "traits" to your object through composition, which makes it a lot more scalable. For sure, a type is an option. I understand the purpose and usefulness of interfaces as a construct, but that wasn't my situation. I need an ORM that properly supports relational data structures like ternary relationships. Interesting for sure! I think class makes it less complex only if you have to stick with inheritance. System/software/information architect, quantum computing enthusiast, gamer, and metalhead. I have never seen this before.

Let's see the following code as example: As you can see is not encapsulated as a part of the class Person.

You can temporarily use the --noStrictGenericChecks flag to get around this in TypeScript 2.4. And it is encouraged by languages like Java and javascript because the structure/prototype is described in the runtime, thus it can be queried a.k.a Reflection. RxJS 6 will have this fixed, but as a temporary workaround, you can use the noStrictGenericChecks compiler option. Okay, this is a more minor annoyance, but it really bugs me. So fa Issue I want to convert current data into 'yyyy-MM-dd' format in .ts file Issue I am having this header which on scroll, I want to change the background to a differ Issue I want to make 2 API calls in Parallel and then the third immediately after that.

I think the problem was not so bad until type enforcement kicks in. I've always found the intellisense for regular JavaScript packages to be a bit flaky for some reason, but it's rock solid with TypeScript.

As far as whether it's really different than a class, I mean yeah, it is. It's even more useful in a service that uses its own methods internally, since ctrl+f is less useful in that case. As mentioned in the post, I need to access static properties of various subclasses of Model, so I need to pass around the classes themselves. Keep in mind, RxJS 6 will have this corrected. This works because of hoisting. They only provide the abilty for other users to inject their own implementation of a pattern. The problem arises when we upgrade Typescript to the latest version, which by now was TypeScript 2.4.1, [ "as we love the upgrades : )" ], and as mentioned by @Jonnysai in his answer and the link provided there, there is a detailed discussion regarding the problem and its fixes.

What's your preferred Node.js testing setup? How would you define Hoisting and when to use it over other constructs? It's nice to see more people embracing TypeScript.

I think you are showing something that worked for AngularJs? Hi Ken, I will start with my appreciation for you taking the time to type in some examples for the discussion. Welcome to the ecosystem, good luck and have fun. In this post I like to write about my experiences with those. Ahh, I see what you mean. Angular 4 application development with Bootstrap 4 and TypeScript, reinstalling rxjs -> npm install rxjs@6 rxjs-compat@6 --save, Now we dont need the ionic-native module - we only need @ionic-native/core.

I'll keep those groups handy. I have faced same error after adding this error resolved. I just feel that functions are first class citizen and works better with Typescript then classes. The difference is the unnecessary complexity which is big on terms of maintainability of code. It removes any benefits you get from using a typed language.

I'll have to think about that one.

You might know what you're passing, but the next developer, and the next one after that, won't know. */, // push some models into the array, including Animal, // code to process command line arguments, // code to initialize an ElasticSearch client, // code to query ElasticSearch for some metrics data, // code to process and format raw results into a custom format, // object of type "function" is created everytime Animal is called, /* That's why I was overriding them. What's the '@' (at symbol) in the Redux @connect decorator? Run, thanks the answer of zmag and Rahul Sharma, it works!

And as you can probably tell by my examples here, I also don't think classes are the best thing for all cases. The code is long and it's already the optimal amount of code to achieve type correctness in your application. In this case, I believe it should return an async function, which returns a promise, which wraps your database object. It gives me that ability to re-use anything anywhere. Once unpublished, this post will become invisible to the public Why not just get used to always use strict mode instead? Edward's example of an object factory has a perfect type and perfect JavaScript encapsulation which is very convenient for people who cares about encapsulation and OOP in general.

I do mean at the program layer, yes. If multiple components need to use something in common, I usually abstract the component to an Angular Service today. Here's a playground example (in a broken state) showing what I mean. Interface defintions are not strictly needed. I'd treat ObjectionJS modules as another "unknown territory" in the application, like localStorage.get, fetch, fs.readFileSync, redisClient.get, etc. Even though TS was born from OOP paradigm, it's actually easier to just use type and namespaced-functions is the form of static methods in a class. I have heard endless good things about TypeScript in the last couple years, but I've never really had a chance to use it. Edward Tam: It is not subjective unless you can point out what can not be achieved without class. That definitely clears up your point quite a lot, and there's a lot less distance between our positions than it seemed at first, so I really appreciate the clarification and your example. Lots of old school JavaScript interviewers will still ask you about "hoisting" which is non-existent by default with the Class. My point is that hoisting is still a fundamental aspect of JavaScript and it's pretty important to understand, or at least be aware of, even if you have to look it up from time to time.

Hopefully that all made sense it's a weird bit of rather esoteric JavaScript knowledge that you can basically look up when you need it. "ctrl+click my way into whichever part I need to read or mess with at the moment". So when I was tasked with writing a new API from scratch at work, I decided to use the opportunity to learn TypeScript by jumping into the deep end. Issue I have created a custom ValidationFn in angular. => a.idColumn().whatIsValidHere) Stick in /shared/ or wherever you keep such things. add this snippet to your app: His solution will leave no other side-effects and is thus great. Let's take a closer look at the example again: You can actually manipulate the reference of this. How to earn 10k per month with 1 time 15k investment? then what is always safe for whatisvalidhere if it's sometimes a string sometimes an array sometimes an Invoice, etc. I just don't blanketly subscribe to the 'toss class support for functions' argument. I am new to Angular2 and trying to get hold of things. Interestingly, I notice that Objection.js actually provides typings, though they seem rather convoluted and maybe more intended for internal library use; what do you think? I found same problem and I solved it by using "rxjs": "5.4.1", "typescript": "~2.4.0" and adding "noStrictGenericChecks": true into tsconfig.json. The only drawback is that I have to import the service in order to reuse the code within it. Example. Regarding passing around classes and subclasses, in your example, modelClass: Model is still and instance of some class extending Model, rather than a class itself. This is definitely a personal preference, but I don't think the relatively minor tradeoff of context-free methods is worth it. I don't really like either; the former feels slightly misleading, but the latter feels incomplete. I am dealing with Typescript for a while now but this sure demystified certain things ^ pretty cool! That really helps understanding your rationale and where our disagreement come from.

In programs with heavy computation DoD helps with creating cache-friendly code, in the javascript environment, performance doesn't seem to increase much, but in terms of readability and extensibility, it really improves them. How do I get around this Subject incorrectly extends Observable error in TypeScript 2.4 and RxJs 5, solved the issues.

damn slow. yes the problem was with It promotes encapsulation in a more clear manner; to me, as well as a default strict mode. Javascript classes are not actually classes and operate quite different from other class-base languages. We could say compilers are syntatic sugar for assembly language too but compilers save time and improve quality. In practical terms, it's deeply subjective which paradigm is more complex. Even if we suppose that classes and functions provide exactly the same capabilities and classes provide no new unique powers, the complexity that matters more in day to day life is the mental complexity for readers of the code.

From the command line of an IDE? Definitely something for me to study. In your example you do not need to override the getter for Id.

This is the parent class method in BaseModel: This is the extending method of Animal model: Typescript infers BaseModel's database getter to be of type void. He/him. I personally don't use them nearly often enough to justify that kind of a change across the board. . It's just my opinion though, you know the lib better and might prove me wrong on this.

Ken; . Totally agree, my biggest frustration with AngularJS is the total lack of intellisense. And that actually brings me to something else that I'd love to hear your feedback on. Why do anything but use the Class? You could practically give unknown or if not possible any (forgive me, lord) to the idColumn and other static method return type. For further actions, you may consider blocking this person and/or reporting abuse. Unfortunately as you've pointed out, it doesn't really have support for TS. This is a pretty long thread at this point lol. Once unsuspended, kenbellows will be able to comment and publish posts again. I didn't realize that was a thing! Templates let you quickly answer FAQs or store snippets for re-use. 2) That's not a Typecript question, that's an object-oriented question. Some developers have an easier time thinking in functional terms and passing objects around between functions. Oh man yes it does, that's exactly what I was looking for! All the functions for individual steps are hoisted to the top of the file so they're immediately available.". The "might be undefined" checks have definitely saved me some time by pointing out places where I need to add a few null checks after, I have always liked being able to spell out my classes in JavaScript; I've often gone to extreme lengths to document JS classes with. DEV Community A constructive and inclusive social network for software developers.

For example, I would rather use "knex" to build the queries wrapped with functions instead of using an ORM (in your case objection) because I feel like it is more straight forward and faster to get things done, and you have more control over what you want to return.

However, function declarations are special because they don't have separate declaration and initialization steps, it's all-in-one, so they get hoisted completely to the top: And const and let are a bit weirder. It is not subjective unless you can point out what can not be achieved without class. pattern to make a mini game (don't laugh), and man it was I didn't realise you could combine new with typeof T params. This is what makes it misleading in an OOP perspective because you would have thought the context is part of the encapsulation in the definition. To fix complaints.

*/, // Using type instead of class because type is zero-cost in the runtime, // called on render on every entity instantiated in world, // assumptions are Dog as an Entity is a mutable object, // meaning in this scenario dog object are not recreated { dog }, // There's an event listener that can be fired outside of the game's main loop, // corrupted data in the database, data is not contractual, // => function x() { console.log('hey!') If it's not an issue any longer, why do interviewers want to test your knowledge of "hoisting" even today? It can help to be able to ask quick questions on or, Awesome, thanks! This Answer collected from stackoverflow and tested by AngularFix community admins, is licensed under, RN: Class static side 'typeof *' incorrectly extends base class static side 'typeof BaseModel, How to fix Angular issue: Cannot read properties of null (reading 'cannotContainSpace'). I'm genuinely anxious to know, because I've recently entered a role where, as I mentioned, I'm training up a few long-time Java devs in the ways of the web, and I'm anxious to avoid any misconceptions. My comment was mostly in response to when you said: Lots of old school JavaScript interviewers will still ask you about "hoisting" which is non-existent by default with the Class. Web feature you don't understand?

So, what worked for me was: Thanks for the complement, now let me disagree with you .

@Ken I would take the shortest, easiest, and safest path that scales both in performance and development. This doesn't have to do with classes vs functions.

I missed that. So as Alan also mentioned in the other reply, I tend to go with functions and closures in order to workaround this hustle.

Pick the run gun against the right monster. Pros and cons, I guess. I'm enjoying TypeScript on the whole, and I'm sure little quirks like this will become natural after a while, but if there is a better way to handle them, I'd love to know! Senior software developer, experienced in .NET development and passionate about learning new software technologies. Making this a typed language you need to expect that it makes more limitations on the code you write to help you avoid any bugs or errors at runtime. expo-sqlite, javascript, react-native, react-native-sqlite-storage, typescript Im a developer that do web applications by day, and games by night. I've run into some cases where a base class declares a method that returns a particular type, but subclasses need to override that method and return a different type. If he wanted to use it for duck typing in his function, then an interface or type would suffice. with respect to the goodness of "hoisting".

Instead, the context is related to where it is called instead. I have to disagree here. "So I wouldn't say that hoisting doesn't matter any more.".

Tell me! With the Class, hoisting is not done and the class body is always in strict mode.

I like Objection a lot; I think it occupies a pretty nice middle ground between query builders and ORMs where it gives you some very nice class-based features out of the box, but still provides low-level access to SQL queries when you need it in a way that many Hibernate-style ORMs do not. The root of the problem is actually the by-the-book OOP usage which doesn't scale for huge projects. React). Have website ?

I would suggest you to do the same and explore more. To return to my specific example, I think there's a lot of value to be found in subclassing a common Model class to represent each table in my database, especially given the use fo static getters to represent metadata like which columns are the primary keys and how different tables are related. This is --noStrictGenericChecks on the command line, or just "noStrictGenericChecks": true in the "compilerOptions" field in tsconfig.json. I understand that in your point of view you could perfectly handle that case, but that's a sample use case.

I wish I had something like: The best I've found so far is to use a rather annoying interface and update it every time I need to use another method from Objection's extensive API, like: This works, but it's rather annoying to have to reinvent the wheel this way. Class static side 'typeof Poodle' incorrectly extends base class static side 'typeof Dog' Let's address the code comparison first. I agree with this comment by Edward Tam.

I would strongly argue that the second is less complex for the developer using the code. @john }, // Now we can call myMethod with either of the two classes above, class field and private class field syntaxes, TypeScript 3.5's feature higher-order type inference, a method I wish I knew about a long time ago.

*/, /* Definitely use only functions if you like that, but this problem still needs to be taken into account, and it is simply about assignment.

It is common in heavy computation. Huh, Record is a pretty handy trick.

Very good question. If you look closely to the problems you are having, they are pretty much all class oriented. Is this really different than a class construct where as you pointed out the syntax doesn't require the function keyword?

This problem is especially painful when you work with frontend code (e.g. Strict mode isn't something I really worry about; I write strict JS by habit at this point, and I especially don't worry about it since I've started using modules, which are also strict mode by default. Let that new paradigm sink in.

One way I still use it all the time is when I write utility scripts. And hey, If all you need is private vars, go for it, but I don't think this approach covers all cases, or even most. Yeah Model isn't my class, it's provided by Objection.js, an ORM library I'm using. ObjectionJS is of a different paradigm, and let it be that way because we can't change how it behaves nor we can put a strict TypeScript rule to it.

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I'll write an article! If each of the static methods are to return the same thing you only need one in the base class. I'm a huge fan of the added intellisense in my IDE (VS Code).

It introduces extra layer of complexity with virtually no gain. And I don't "blindly subscribe" to the idea.

So, I wrote this article a couple months ago now, and since then I've developed my project into a pretty sizable codebase, still using Objection with TypeScript. If an interface or type is used and he wanted to create an instance of the Model class, using an interface or type would not work. Also, check out io-ts if you haven't, it's a cool lib. 2. Tragically, I also still work on an old Angular.js 1.x project, and we do something similar to structure our Factory and Service files: In this case, the returned object at the top of the service acts as a sort of Table of Contents for the service. "Is a" object relationships are the tightest form of coupling that exists. The parent must be a type of base. But you can see from the example I gave, there is not much different in outcome from a readability perspective, which is what I mean by virtually no gain. Regardless, that was fun discussion and I think I learnt something from it :), Definitely Thanks to everyone in this thread for the back and forth, it was a good discussion and we made it out without any flames, "This is the sort of layout I like to use for my scripts because I can open up the file and immediately see an outline of the main steps of the script, then ctrl+click my way into whichever part I need to read or mess with at the moment. Built on Forem the open source software that powers DEV and other inclusive communities. Have site? Once unpublished, all posts by kenbellows will become hidden and only accessible to themselves.

You can run it and see the error. You had asked "How would you restructure that program to use a class?" So I wouldn't say that hoisting doesn't matter any more.

This is not ideal either as you might not get some type errors reported. I definitely agree in general with composition-over-inheritance approaches like the one you've demonstrated, especially if you have a wide variety of features that need to be combined depending on circumstance. You can no longer do = 'Fido' to rename your dog. The second point, absolutely. Interesting idea with DOD Alan, this paradigm seems interestingly common in heavy computation. Do you mean at the program layer? Only arrays and iterables are allowed in Angular-11 Application, Why is @angular/core/core has no exported member 'FactoryDeclaration'. Class in JS is just merely syntactic sugar.