Welcome! Please see the About page for a little more info on how this works.
In online repl at https://clojurescript.io/ you get this behaviour:
cljs.user=> (array-map 1 2 1 234)
Key "1" should have value 234, according to spec. In clojure it works as expected.
clojurescript.io is not an "official" project and by this time is fairly outdated. The last update was done several years ago. See https://github.com/Lambda-X/cljs-repl-web
It works as expected if you use a more current CLJS version.