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If a JavaScript type is inferred, "base" properties are not considered. A specific example is {{js/document}}, which gets inferred as {{js/HTMLDocument}}. If code makes use of any of the base properties, then an inference warning will get triggered, even though {{:advanced}} compilation is fine.

(ns test.infer)

(set! *warn-on-infer* true)

(.-documentElement js/document)

$ clj -m cljs.main -co '{:infer-externs true}' -c test.infer
WARNING: Cannot resolve property documentElement for inferred type js/HTMLDocument in expression (. js/document -documentElement) at line 5 /Users/mfikes/Desktop/test-infer/src/test/infer.cljs

If you add {{-O advanced}} you can confirm that {{documentElement}} survives into the compiled artifact without being mangled.

Also, you can work around the issue by hinting the target as being the base type:

(.-documentElement ^js/Document js/document)

Perhaps there is some way to make use of the "extends" metadata in the externs in cases like these to check base types before emitting a warning (or by inferring the base type based on the property being accessed). Here is the extends metadata of interest in the example above: https://github.com/google/closure-compiler/blob/50713dceb16b369f8f317e5b49e8a9dec2b47496/externs/browser/w3c_dom2.js#L171

1 Answer

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Reference: https://clojure.atlassian.net/browse/CLJS-2928 (reported by mfikes)
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