ClojureScript :advanced optimizations — keeping JS-interop property names intact without an externs file

Answer

Under :optimizations :advanced the Google Closure Compiler renames property names that are accessed via dot notation (e.g. (.foo js-lib) or js/lib.foo). To keep those names intact you must either protect them with an externs file, use string‑key access via goog.object/get (and goog.object/set for writes), or give the compiler enough type information to infer externs. The standard ClojureScript compiler does not infer externs from plain js/ usage; shadow‑cljs does this automatically for npm dependencies, which often removes the need for a hand‑written externs file.

Confirmed facts

• Dot‑interop (. or js/) is renamed unless the name appears in an externs file.
• (goog.object/get obj "propName") protects that read because the string literal is not renamed; writes need goog.object/set or aset with a string key.
• ^:export only protects names you define in ClojureScript for external consumption; it does not protect third‑party property names.
• The standard cljs.main/clojurescript pipeline does not infer externs from js/ unless you add ^js hints and set :infer-externs true.
• shadow‑cljs processes npm dependencies and enables externs inference by default, automatically generating externs for many js/ usages (both hinted and many unhinted).

Likely explanation

If you rely on plain js/ dot access without hints, the compiler will treat those properties as internal and rename them, leading to runtime errors like "undefined is not a function" only in the advanced build. Using goog.object/get avoids renaming per‑access, while adding ^js hints lets the compiler infer externs (standard) or lets shadow‑cljs do it automatically.

Steps needed for this case

1. Standard ClojureScript compiler:
   • Option A: Provide an externs file that lists all third‑party property names you use and add it via :externs.
   • Option B: Add ^js hints to every js/ value you interop with and set :infer-externs true in your build config.
   • Option C: Replace dot access with goog.object/get (reads) and goog.object/set or aset (writes) using string keys.

1. shadow‑cljs:
   • Most npm‑based JS interop works without an externs file because shadow‑cljs infers them automatically.
   • Check the build report or the generated externs.js to verify that the properties you rely on are present.
   • If a property is missing, add a ^js hint to the corresponding js/ value or supply a small externs file for that library.

Missing diagnostic detail

Are you using ^js type hints on the js/ values you interop with? Knowing this determines whether you need to add hints, rely on inference, or fall back to an externs file.