Ember.js has three built in logging facilities defined in the Ember namespace. These are in addition to those contained in the Ember.Application namespace that we explored in my last post, Logging the Magic in Ember.js.
Log Version
The first is LOG_VERSION, which is set to appear once on page load.
Ember.LOG_VERSION = true;
It produces helpful information about the version of Ember.js and its dependencies:
DEBUG: -------------------------------
DEBUG: Ember.VERSION : 1.0.0-rc.5
DEBUG: Handlebars.VERSION : 1.0.0-rc.4
DEBUG: jQuery.VERSION : 2.0.0
DEBUG: -------------------------------
Log Bindings
You will get most mileage out of LOG_BINDINGS given how integral bindings are to Ember applications.
Ember.LOG_BINDINGS: true;
Now, when a property which is bound to another is changed, Ember triggers a log message to the console with relevant details.
Consider this simple example concerning a proxy object, which property appName is bound to the name property of our Ember application App.
app.js
var App = Ember.Application.create({
name: "EmberWatch"
});
App.proxy = Ember.Object.create({
appNameBinding: 'App.name'
});
Changing either value provokes a log message. Notice how Ember includes the data flow direction, indicating which property changed to fire the corresponding update.
> App.set('name', "EmberWatch Blog");
Ember.Binding<ember344>(App.name -> appName) -> EmberWatch Blog
> App.proxy.set('appName', "EmberWatch");
Ember.Binding<ember344>(App.name -> appName) <- EmberWatch
Log Stack Trace on Deprecation
Ember logs a deprecation warning to the console each time that you call a method that has been deprecated in the API. This is what it looks like for Ember.Button which has been superceded by the action Handlebars helper:
DEPRECATION: Ember.Button is deprecated and will be removed from future releases. Consider using the `action` helper.
With LOG_STACKTRACE_ON_DEPRECATION enabled:
Ember.LOG_STACKTRACE_ON_DEPRECATION: true;
Ember now prints the stack trace with the warning:
DEPRECATION: Ember.Button is deprecated and will be removed from future releases. Consider using the `action` helper. at Ember.Button.Ember.View.extend.init
(http://localhost:4000/assets/ember.js:22412:11) at superWrapper [as init]
(http://localhost:4000/assets/ember.js:1060:16) at new Class
(http://localhost:4000/assets/ember.js:11298:15) at Function.Mixin.create.create [as create]
(http://localhost:4000/assets/ember.js:11597:12) at Ember.View.Ember.CoreView.extend.createChildView
(http://localhost:4000/assets/ember.js:16950:19) at Object.Ember.merge.appendChild
(http://localhost:4000/assets/ember.js:17452:22) at Ember.View.Ember.CoreView.extend.appendChild
(http://localhost:4000/assets/ember.js:16830:30) at EmberHandlebars.ViewHelper.Ember.Object.create.helper
(http://localhost:4000/assets/ember.js:20958:17) at get
(http://localhost:4000/assets/ember.js:21136:37)
Conclusion
The in-built logging capabilities in the Ember namespace might not be as useful as those in Ember.Application but it is helpful to be aware of them. The LOG_BINDINGS setting will end up being the most useful of the three. ■