Browser capabilities - check if object exists in ClojureScript

Question

What is the way to test if something exists in ClojureScript ? For instance, I am trying to access the browser geolocation API. In javascript, I would do a simple check like that :

// check for Geolocation support
if (navigator.geolocation) {
  console.log('Geolocation is supported!');
}
else {
  console.log('Geolocation is not supported for this Browser/OS version yet.');
}

But translating it to ClojureScript, I get an error :

(if (js/navigator.geolocation)  ;; Uncaught TypeError: navigator.geolocation is not a function
   (println "Geolocation is supported")
   (println "Geolocation is not supported"))

What is the proper way to check browser capabilities in ClojureScript ?

ClojureMostly · Accepted Answer · 2017-06-24 05:16:31Z

7

There is multiple options:

exists?: http://dev.clojure.org/jira/browse/CLJS-495

Only exists in clojurescript and not clojure. If you look at the macro in core.cljc you'll see it's just a if( typeof ... !== 'undefined' ). Example use :

   (if (exists? js/navigator.geolocation)
      (println "Geolocation is supported"))
      (println "Geolocation is not supported"))

(js-in "geolocation" js/window) which expands to "geolocation" in windows.
(undefined? js/window.geolocation) which expands to void 0 === window.geolocation

IMO, the right one is js-in.

edited Jun 24, 2017 at 5:16

answered Aug 14, 2015 at 14:39

ClojureMostly

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1 Comment

nha Over a year ago

I added an example use, as it was the first use of :require-macro for me. Hope that's ok, thanks.

nha · Accepted Answer · 2015-08-14 12:54:00Z

1

For now, I am using :

(if (not (nil? js/navigator.geolocation))
    (println "Geolocation is supported")
    (println "Geolocation is not supported"))

Not sure if this idiomatic/cover all use cases, I would gladly accept another answer with a proper explanation.

answered Aug 14, 2015 at 12:54

nha

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