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day8 / re-frame

A ClojureScript framework for building user interfaces, leveraging React
http://day8.github.io/re-frame/
MIT License
5.44k stars 716 forks source link

Fix a warning in todomvc #673

Closed miles-d closed 3 years ago

miles-d commented 3 years ago

Add a type hint to fix Cannot infer target type in expression (. event -token).

I did fresh installation of java, Clojure, and Leiningen on Linux, as directed per instructions by following the links on https://github.com/day8/re-frame/tree/master/examples/todomvc.

Leiningen version: Leiningen 2.9.5 on Java 11.0.10 OpenJDK 64-Bit Server VM

When running lein watch, I get this at the end of the output, and the warning is there on every file save:

[:client] Configuring build.
[:client] Compiling ...
[:client] Build completed. (216 files, 1 compiled, 1 warnings, 3.03s)

------ WARNING #1 - :infer-warning ---------------------------------------------                                     
 File: /home/mdr/proj/oss/re-frame/examples/todomvc/src/todomvc/core.cljs:39:53
--------------------------------------------------------------------------------
  36 | (defonce history
  37 |   (doto (History.)
  38 |     (events/listen EventType.NAVIGATE
  39 |                    (fn [event] (secretary/dispatch! (.-token event))))
-----------------------------------------------------------^--------------------
 Cannot infer target type in expression (. event -token)
--------------------------------------------------------------------------------                                     
  40 |     (.setEnabled true)))
  41 | 
  42 | 
  43 | ;; -- Entry Point -------------------------------------------------------------
--------------------------------------------------------------------------------

Of course it's not a biggie, it won't prevent me (or anybody else) from exploring re-frame, but I believe it's good to keep the onboarding experience frictionless.

I didn't understand the warning message, but a quick search pointed me to externs and type hints: https://clojurescript.org/guides/externs https://gist.github.com/swannodette/4fc9ccc13f62c66456daf19c47692799

I know next to nothing about externs and type hints in ClojureScript, but it seems that annotating event in fn on line 39 with the type below fixes the warning. https://google.github.io/closure-library/api/goog.History.Event.html

superstructor commented 3 years ago

Thanks @miles-d 👍