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TypeScript 3.7

typescriptlang.org

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Re: TypeScript 3.7

#121

Post by [deleted] »

vikingcaffiene wrote: post #109
paulddraper wrote: post #104

Earlier quoted context omitted.

&& ?. || ?? It's a shame JS at the beginning doubled down on the "billon dollar mistake" [1] with two(!) kinds of NULL instead of just using Maybe/Option. Ah well, if it were good it wouldn't be popular :/ [1] https://www.lucidchart.com/techblog/2015/08/31/the-worst-mis...

Sorry, JS? While JS might get this stuff one day, these language features are for TypeScript which is its own language. It's strongly typed and just happens to interop with and in some scenarios transpile down to JavaScript. It's whole existence is to deal with that billion dollar mistake you mentioned. Speaking of which, optional chaining and null coalescence are core language features of some very good languages. K…

[deleted]

Re: TypeScript 3.7

#122

Post by autora »

vikingcaffiene wrote: post #109
paulddraper wrote: post #104

Earlier quoted context omitted.

&& ?. || ?? It's a shame JS at the beginning doubled down on the "billon dollar mistake" [1] with two(!) kinds of NULL instead of just using Maybe/Option. Ah well, if it were good it wouldn't be popular :/ [1] https://www.lucidchart.com/techblog/2015/08/31/the-worst-mis...

Sorry, JS? While JS might get this stuff one day, these language features are for TypeScript which is its own language. It's strongly typed and just happens to interop with and in some scenarios transpile down to JavaScript. It's whole existence is to deal with that billion dollar mistake you mentioned. Speaking of which, optional chaining and null coalescence are core language features of some very good languages. K…

> just happens to interop with

It does not interop with JavaScript.

> and in some scenarios transpile down to JavaScript

It always transpiles to JavaScript and always runs as JavaScript. There is no such thing as a TypeScript runtime engine.

TypeScript is a superset of JavaScript. Therefore the OP's point is still valid. Any "mistakes" JavaScript might have made about having null AND undefined are also issues for TypeScript.

Re: TypeScript 3.7

#123

Post by MaulingMonkey »

knocte wrote: post #103

From the snippets in the release notes: ``` function dispatch(x: string | number): SomeType { if (typeof x === "string") { return doThingWithString(x); } else if (typeof x === "number") { return doThingWithNumber(x); } process.exit(1); } ``` It's very embarrassing in my opinion that they haven't done anything yet against having these horrible kind of type checking; comparing against a string that has the type name? "…

You can define your own type guards:

    function isString(x: any): x is string {
        return typeof x === "string";
    }
    
    function isNumber(x: any): x is number {
        return typeof x === "number";
    }
    
    function dispatch(x: string | number): SomeType {
        if (isString(x)) {
            doThingWithString(x);
        } else if (isNumber(x)) {
            doThingWithNumber(x);
        }
        process.exit(1);
    }
TypeScript seeks to manage JavaScript's horrors, but importantly, it does not seek to hide them behind leaky abstractions. This is not an embarassment, but TypeScript's strength and weakness.

There is a long list of other languages that compile down to JavaScript or WASM, if you want a language built from clean foundations. But if you want to add gradual typing as a means of slowly reigning in your existing JavaScript behemoth? There is only one TypeScript.

Re: TypeScript 3.7

#124

Post by Zarel »

autora wrote: post #122
vikingcaffiene wrote: post #109

Earlier quoted context omitted.

Sorry, JS? While JS might get this stuff one day, these language features are for TypeScript which is its own language. It's strongly typed and just happens to interop with and in some scenarios transpile down to JavaScript. It's whole existence is to deal with that billion dollar mistake you mentioned. Speaking of which, optional chaining and null coalescence are core language features of some very good languages. K…

> just happens to interop with It does not interop with JavaScript. > and in some scenarios transpile down to JavaScript It always transpiles to JavaScript and always runs as JavaScript. There is no such thing as a TypeScript runtime engine. TypeScript is a superset of JavaScript. Therefore the OP's point is still valid. Any "mistakes" JavaScript might have made about having null AND undefined are also issues for Typ…

> It does not interop with JavaScript.

I don't know what you mean here, but it is certainly possible for TypeScript code to use JavaScript libraries and vice versa, which is presumably what most people mean by "TypeScript interops with JavaScript".

> It always transpiles to JavaScript and always runs as JavaScript.

Technically false... https://assemblyscript.org

> TypeScript is a superset of JavaScript. Therefore the OP's point is still valid. Any "mistakes" JavaScript might have made about having null AND undefined are also issues for TypeScript.

TypeScript adds type checking to JavaScript. The Million Dollar Mistake is having unchecked nulls; TypeScript supports checked nulls so it's not an issue. TypeScript's nulls are much more similar to Maybe/Option than unchecked nulls.

Re: TypeScript 3.7

#125

Post by ygra »

desert_boi wrote: post #97
nikeee wrote: post #79

Earlier quoted context omitted.

You can also get rid of `if(result){}` by setting the return type of "doSomethingWithErr" to "never": function doSomethingWithErr(err: any): never { throw new Error("Oops"); } let result: SomeType; try { result = await funcThatReturnSomeType(); } catch (err) { doSomethingWithErr(err); } // because doSomethingWithErr has return type "never", result will be definitely assigned. doSomething(result); ..or just return in…

Interestingly when I was encountering this myself recently, I discovered that JS finally blocks can return after a function has nominally already returned. Consider the following closure. (() => { try { // finally will return prior to this console.log console.log('this try was executed and the return ignored') return 'try block' } catch (e) { return 'error block' } finally { return 'finally block' } })()

It's probably either this behavior or a statement in the finally block that doesn't run, even though it's guaranteed to. Either way, some assumption of normal program behavior is invalidated.

Unless one goes the PowerShell way and just forbids returning from finally.

Re: TypeScript 3.7

#126

Post by autora »

Zarel wrote: post #124
autora wrote: post #122

Earlier quoted context omitted.

> just happens to interop with It does not interop with JavaScript. > and in some scenarios transpile down to JavaScript It always transpiles to JavaScript and always runs as JavaScript. There is no such thing as a TypeScript runtime engine. TypeScript is a superset of JavaScript. Therefore the OP's point is still valid. Any "mistakes" JavaScript might have made about having null AND undefined are also issues for Typ…

> It does not interop with JavaScript. I don't know what you mean here, but it is certainly possible for TypeScript code to use JavaScript libraries and vice versa, which is presumably what most people mean by "TypeScript interops with JavaScript". > It always transpiles to JavaScript and always runs as JavaScript. Technically false... https://assemblyscript.org > TypeScript is a superset of JavaScript. Therefore the…

> I don't know what you mean here, but it is certainly possible for TypeScript code to use JavaScript libraries and vice versa, which is presumably what most people mean by "TypeScript interops with JavaScript".

Ah, I can see what you/they mean by that. The point I was trying to get across was: TypeScript doesn't exist when code is actually executing (which is what I think of as interop - it's happening at execution time.) At execution time - it's all just JavaScript.

I have found (working in a TypeScript team currently) that this fact is ignored, primarily by people who "look down" on JavaScript, but it is a VERY important point to remember when you are writing TypeScript, mostly because it's important to remember there is only compile time type checking not run time.

> Technically false... https://assemblyscript.org

Heh, yes - as soon as I posted I realised that was silly. The word "always" is almost "always" incorrect! I should have said: "It usually transpiles to JavaScript and usually runs as JavaScript"

> The Million Dollar Mistake is having unchecked nulls; TypeScript supports checked nulls so it's not an issue. TypeScript's nulls are much more similar to Maybe/Option than unchecked nulls

Good point in theory but my practical experience hasn't borne this out. That is because TypeScript is an "optionally typed" language and it hasn't been true in practice because of excessive use of explicit or implicit "any"s.

Re: TypeScript 3.7

#127

Post by KuhlMensch »

autora wrote: post #122
vikingcaffiene wrote: post #109

Earlier quoted context omitted.

Sorry, JS? While JS might get this stuff one day, these language features are for TypeScript which is its own language. It's strongly typed and just happens to interop with and in some scenarios transpile down to JavaScript. It's whole existence is to deal with that billion dollar mistake you mentioned. Speaking of which, optional chaining and null coalescence are core language features of some very good languages. K…

> just happens to interop with It does not interop with JavaScript. > and in some scenarios transpile down to JavaScript It always transpiles to JavaScript and always runs as JavaScript. There is no such thing as a TypeScript runtime engine. TypeScript is a superset of JavaScript. Therefore the OP's point is still valid. Any "mistakes" JavaScript might have made about having null AND undefined are also issues for Typ…

This does not necessarily invalidate your wider points, but just FYI:

> It does not interop with JavaScript.

Hm, this depends on your definition of "interop". My JavaScript and TypeScript are languages that exchange information. The execution model ultimately involves JavaScript when I use tsc, but ultimately it also includes an interpreter. My user-space syntax doesn't care.

> There is no such thing as a TypeScript runtime engine.

Not being glib, just a heaps up: https://github.com/denoland/deno

Re: TypeScript 3.7

#128

Post by paulddraper »

vikingcaffiene wrote: post #109
paulddraper wrote: post #104

Earlier quoted context omitted.

&& ?. || ?? It's a shame JS at the beginning doubled down on the "billon dollar mistake" [1] with two(!) kinds of NULL instead of just using Maybe/Option. Ah well, if it were good it wouldn't be popular :/ [1] https://www.lucidchart.com/techblog/2015/08/31/the-worst-mis...

Sorry, JS? While JS might get this stuff one day, these language features are for TypeScript which is its own language. It's strongly typed and just happens to interop with and in some scenarios transpile down to JavaScript. It's whole existence is to deal with that billion dollar mistake you mentioned. Speaking of which, optional chaining and null coalescence are core language features of some very good languages. K…

> optional chaining and null coalescence are core language features of some very good languages

They are features of Maybe/Option too, just in a more consistent extensible way.

    val a = Some(thing)
    val b = a.flatMap(_.part).flatMap(_.subpart)

    val c = Some(None) // look Ma! a nested option!
> While JS might get this stuff one day

I appreciate the attempt at pedantry, but TypeScript general only implements JS language features or TC39 Stage 3 proposals.

> I hope they do the pipe operator next!

Great example. After many hundreds of upvotes, the status is "waiting for TC39". [1] I.e. it will not be implemented until JS has it or is close to having it.

TypeScript is typed JavaScript, end of story.

[1] https://github.com/Microsoft/TypeScript/issues/17718

Re: TypeScript 3.7

#129

Post by Zarel »

munificent wrote: post #69
grapehut wrote: post #41

Earlier quoted context omitted.

Definitely. It's a shame that dart gets so much unwarranted hate. I mean, I also think it's an absolutely awful language but it's really proven to be a valuable source of data for what other programming languages should do and perhaps more importantly: not do. I really hope we see a lot more things like Dart, and not so much negativity.

Depending on when you last looked at Dart, there's a good chance we've either fixed or are fixing the things you hate about it. What didn't you like?

Personally, I'm just waiting for non-nullable types. After getting used to them, it's hard to imagine going back to a language that doesn't have them.

Re: TypeScript 3.7

#130

Post by [deleted] »

vikingcaffiene wrote: post #109
paulddraper wrote: post #104

Earlier quoted context omitted.

&& ?. || ?? It's a shame JS at the beginning doubled down on the "billon dollar mistake" [1] with two(!) kinds of NULL instead of just using Maybe/Option. Ah well, if it were good it wouldn't be popular :/ [1] https://www.lucidchart.com/techblog/2015/08/31/the-worst-mis...

Sorry, JS? While JS might get this stuff one day, these language features are for TypeScript which is its own language. It's strongly typed and just happens to interop with and in some scenarios transpile down to JavaScript. It's whole existence is to deal with that billion dollar mistake you mentioned. Speaking of which, optional chaining and null coalescence are core language features of some very good languages. K…

[deleted]
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