Use default externs to enhance type inference

Question

Currently we process the default externs and this collect type information for many standard JavaScript APIs. We could use this to understand cases like (.-length some-string) and infer that it will return a number. This one probably requires the Mike Files Clojure predicate inference work to be practical.

Answer 1

_Comment made by: mfikes_

Predicate-induced inference has landed on master (CLJS-2866).

David has left a comment in the code showing how this might be leveraged: https://github.com/clojure/clojurescript/blob/f97d766defd02f7d43abd37e3e9b04790a521b1e/src/main/clojure/cljs/externs.clj#L165-L172

As an aside, this ticket may alleviate the need for explicit {{^string}} hints on {{subs}} (CLJS-2868).

Answer 2

Reference: https://clojure.atlassian.net/browse/CLJS-2987 (reported by dnolen)