This question can be best explained with an example:
;; create a basic om app.
lein new mies-om om-tut
lein cljsbuild auto.
Then paste in the following code (in core.cljs)
(ns om-tut.core
(:require [om.core :as om :include-macros true]
[om.dom :as dom :include-macros true]))
(def app-state (atom {:text "Hello world!"}))
(om/root
(fn [app owner]
(reify
om/IWillMount
(will-mount [_]
(om/update! app :text "Success!!!"))
om/IRender
(render [_]
(dom/div nil (app :text ))
)))
app-state
{:target (. js/document (getElementById "app"))})
The code in will-mount is actually being executed, if you drop in a println function, then you'll see that. What is not clear is why the rendering loop is called only once. On the other hand, if you wrap the om/update! within a go block, then it works as expected:
;; add [org.clojure/core.async "0.1.346.0-17112a-alpha"] to your deps in project.clj
(ns om-tut.core
(:require-macros [cljs.core.async.macros :refer [go]])
(:require [om.core :as om :include-macros true]
[cljs.core.async :refer [put! chan <! to-chan close!]]
[om.dom :as dom :include-macros true]))
(def app-state (atom {:text "Hello world!"}))
(om/root
(fn [app owner]
(reify
om/IWillMount
(will-mount [_]
(go
(om/update! app :text "Success!!")))
om/IRender
(render [_]
(dom/div nil (app :text )))))
app-state
{:target (. js/document (getElementById "app"))})
The question is: Why does will-mount not trigger a new rendering loop, since I update app state? I like to use go blocks when I need them, but I don't see why I am forced to wrap this simple example in a block.
It think that will-mount is not a good place to update cursor. Calling om/build with the :fn option will do what you're trying to achieve.
Component is rendered only once, with the updated cursor.
(om/build mycomponent data {:fn #(assoc % :text "Success !")})