Implementing an ajax call in clojurescript - ajax

Question

I'm new to clojurescript and would like to do a deeper dive by implementing a previously written application purely in clojurescript, but am at a loss with respect to to implement an ajax call. Can anyone point me to an example online or provide me with a code snippet or two?

Answer 1

January 22, 2016 update
Although it still works, the original answer is from a time when there was a general lack of ClojureScript solutions with more than 1 contributor. Rather than leveraging XhrIo directly, definitely consider using a well-maintained, feature-rich solution that wrappers it instead like cljs-ajax, as suggested by Mikhail D below!
Okay, So given that Clojurescript leverages Google's Closure JavaScript library, a quick search of the Closure Documentation yielded xhrIo as the proper method for generating AJAX calls:
Example using Closure's Asynchronous XMLHttpRequests with XhrIo
goog.net.XhrIo.send(url, opt_callback, opt_method, opt_content,
opt_headers, opt_timeoutInterval)
A quick review of the Clojurescript source revealed the following function:
From src/cljs/clojure/browser/net.cljs in clojure / clojurescript
(defn xhr-connection
"Returns an XhrIo connection"
[]
(goog.net.XhrIo.))
So something along the lines of this should have the intended results:
(def xhr xhr-connection)
(defn myCallback [replyValue]
... Do Something with replyValue
... for example: (someJsonFunc (.getResponseJson (.target replyValue))))
(defn ajax-json [url]
(.send xhr url myCallback))
For JSONP, you can do something similar using the goog.net.Jsonp. See the link for details:
JSONP Closure API
Hope someone finds this helpful!

Answer 2

An another viable option could be https://github.com/JulianBirch/cljs-ajax
Since it's designed for ClojureScript, the syntax looks clearer and simpler. It also supports a lot of features out of the box (for example: transit, edn and json formats).
Some examples from a README:
(ns foo
(:require [ajax.core :refer [GET POST]]))
...
(GET "/hello" {:handler handler
:error-handler error-handler})
(POST "/send-message"
{:params {:message "Hello World"
:user "Bob"}
:handler handler
:error-handler error-handler})

Answer 3

The way I did it is slightly different. I don't know why the way that Marc suggested in his answer didn't work for me. Hopefully this is also useful.
I used goog.net.XhrIo directly, rather than the xhr-connection wrapper.
(defn callback [reply]
(let [v (js->clj (.getResponseJson (.-target reply)))] ;v is a Clojure data structure
(your-function-here v)))
(.send goog.net.XhrIo url callback)
The main difference that I can see is that I've used .-target to get the property of the JSON object, rather than calling target.
It's worth noting that maps in v that have been created from JSON objects are keyed by strings not keywords.