Why does typescript not accept `text() && text().length === x` in solid-start?

Is anyone aware why typescript complains about

  text() && text().length === 6

  text() && text().length === 6

in a project with the tsconfig.json that comes with the solid-start template? (E.g. typescript complains I should use text()?.length but it didn't in other projects with solid.js) I swear I had solid.js applications where the ts compiler correctly deduced that I checked that text() is non-falsy? EDIT: "typescript": "^4.9.4"

6 Replies

apollo79•2y ago

The problem here is, that a function can return something different for each call, so ts won't allow this.

BersaelorOP•2y ago

ok, so probably the ts compiler is just broken in my other ts project yeah, gotta use text()?.length === 6 then

apollo79•2y ago

There are multiple solutions to this afaik: 1. You can assign the result to a variable and check it 2. You can use the non-null-assertion operator ! 3. You can write a check function with return type T is ... Or yes, you can use ?. 👍

BersaelorOP•2y ago

1. You can assign the result to a variable and check it

Yeah, thats what I usually do, it's just so verbose compared to other environments. In swift for example we can do

if let value = someOptional() {
  use(value)
}

if let value = someOptional() {
  use(value)
}

where in ts I have to do

const value = someOptional()
if (value) {
  use(value);
}

const value = someOptional()
if (value) {
  use(value);
}

apollo79•2y ago

Yes, that is true But I see no problem with using the non-null-assertion operator if you checked it before Or writing a check function if it feels less verbose

bigmistqke•2y ago

I have this utility function I use sometimes when(signal()).then(signal => ...)

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Why does typescript not accept `text() && text().length === x` in solid-start?