Anyone knows what kind of checks the compiler performs with "js" function (<https://kotlinlang.org/a...

# javascript

[Robert Jaros]

Anyone knows what kind of checks the compiler performs with "js" function (https://kotlinlang.org/api/latest/jvm/stdlib/kotlin.js/js.html#js)? I'm experimenting and keep getting "JavaScript: syntax error" at compile time.

[altavir]

I think it just inlines js code. You can run whatever string you are inlining with any js checked. Maybe just paste in in a separate js file or scratch

[Robert Jaros]

the compiler definitely performs some checks

[Robert Jaros]

i can do

js("blahblah")

and it compiles fine

[Robert Jaros]

but I can't do

js("import")

because I have JavaScript:Syntax error

[Robert Jaros]

at compile time

[altavir]

Yep. I think it uses some kind of js syntax check during the compilation. I did not know about it, but it is good to have.

[Robert Jaros]

I can't do

js("impor t")

because it gives JavaScript: missing ; before statement

[Robert Jaros]

I've tried to find the sources but its hard 🙂

[Svyatoslav Kuzmich [JB]]

It has to be valid JavaScript expression or a list of statements.
If you want to look at sources, good place to start would be parseJsCode at kotlin/js/js.translator/src/org/jetbrains/kotlin/js/translate/reference/CallExpressionTranslator.java

[gildor]

Do you use DCE? There is a bug in DCE that doesn't allow to use import() function:
https://youtrack.jetbrains.com/issue/KT-28523

[Robert Jaros]

@Svyatoslav Kuzmich [JB] So why is

js("blahblah")

ok and

js("import")

not ok?

[Robert Jaros]

@gildor There is no DCE at this point - this is Kotlin compile-time error.

[Svyatoslav Kuzmich [JB]]

I’m not exactly sure, i’ll speculate that import is a reserved word and standalone import; would be a syntax error since ES5

[Robert Jaros]

I think this check is somewhere in here: js/js.parser/src/com/google/gwt/dev/js/rhino/Parser.java

[Robert Jaros]

but after looking at this package I have no idea what makes the "import" keyword so special 😉

[Svyatoslav Kuzmich [JB]]

com/google/gwt/dev/js/rhino/TokenStream.java:483 KEYWORDS.put("import", IMPORT);

[Robert Jaros]

probably just the fact it is not processed in the statementHelper method at all 🙂

[Robert Jaros]

@Svyatoslav Kuzmich [JB] Other keywords defined in the same place work fine. E.g.

js("switch (d) { case 1: break}")

is correct.

[Svyatoslav Kuzmich [JB]]

js("switch") does not work tho

[Robert Jaros]

but gives different error message

[Robert Jaros]

the statementHelper method in Parser.java is the key

[Robert Jaros]

import support is missing there

[Robert Jaros]

it's processed by the default: branch and reportError(ts, "msg.syntax"); is the result

[Robert Jaros]

maybe it's not too hard to fix 😉

[Robert Jaros]

But in the meantime i know it's not necessary at all to play with js("import") 😉

[Robert Jaros]

KT-28523 gives better alternative

[Robert Jaros]

And i hope the bug itself will be fixed soon

[Robert Jaros]

thx @Svyatoslav Kuzmich [JB] for help