"banner" must be a string

[HomyeeKing]

here's the reproduce link

in transform mode, will get the error

but the build mode is fine

[evanw]

You’re getting an error that says “banner must be a string” in transform mode because “banner” must be a string in transform mode. The error message is correct. You need you fix your code to address the error message.

[HomyeeKing]

OK. I think maybe the docs here should show the difference or it might cause confuse

and also no idea what's the proper string format, is it like "js=//comment"?

[HomyeeKing]

And I wonder if esbuild can handle the format internally? It's very unconvinient both write a string here and the one config in two format

[hyrious]

The format is infered by --loader=js|css from options.

[evanw]

And I wonder if esbuild can handle the format internally? It's very unconvinient both write a string here and the one config in two format

The rationale is that the build API can handle multiple files while the transform API only ever handles a single string. Specifying both banner types to the transform API is arguably confusing because that involves specifying something that cannot possibly affect the output. So instead the transform API only takes a single string, which is the string that the API uses. I agree that the documentation should provide examples for both APIs.