Where should I set defaults on components with attributeBindings? - ember.js

Question

I have a component {{upload-image src=foo.bar}}. When foo.bar is falsy I want to give it a different value. I setting the value in init like so:
import Ember from 'ember';
export default Ember.Component.extend({
attributeBindings: ['src'],
tagName: 'img',
init: function(){
this.set('src', 'http://www.placecage.com/40/40');
this._super();
this.set('src', 'http://www.placecage.com/40/40');
},
click: function(){
console.log(this.get('src'));
}
});
However it doesn't work. The image gets rendered with the value I pass in, not the new one. When I click the image it does log the placecage image. Instead if I try to override it later on say didInsertElement it works as expected:
import Ember from 'ember';
export default Ember.Component.extend({
attributeBindings: ['src'],
tagName: 'img',
didInsertElement: function(){
this.set('src', 'http://www.placecage.com/40/40');
},
click: function(){
console.log(this.get('src'));
}
});
It seems a bit silly to have it render out and only then be able to change the value causing (I presume) a re-render. What's the appropriate place to check if src is falsy and set it to a default and get the expected results?

Answer 1

In Ember 1.13 you can do that in
attributeBindings: ['src:src'],
didInitAttrs() {
this.set('src', <new value>);
}
Or you could do the falsy logic outside of the component and pass it in.

Answer 2

I would create another property defined as follows:
effectiveSrc: function() {
return this.get('src') || 'http://www.placecage.com/40/40';
}.property('src')
then use effectiveSrc in your logic and templates.
Another alternative is to give src a default:
src: 'http://www.placecage.com/40/40'
Then when calling your template, omit src if its value is falsy, something like
{{#if foo.bar}}
{{upload-image src=foo.bar}}
{{else}}
{{upload-image}}
{{/if}}
The following might also work, need to try it:
{{upload-image src=(if foo.bar foo.bar)}}

Answer 3

With ember 2.x (I've tested with 2.4.2, 2.4.3 and 2.5.0), I've achieved this functionality with the mentioned default by torazaburro :
export default Ember.Component.extend({
attributeBindings: ['src'],
tagName: 'img',
src: 'http://www.placecage.com/40/40',
click() {
console.log(this.get('src'));
}
}
And the templates:
{{upload-image src="http://cdn.sstatic.net/Sites/stackoverflow/img/apple-touch-icon.png"}}
{{upload-image}}
The Twiddle to test it

Answer 4

There's an open issue over on Github https://github.com/emberjs/ember.js/issues/11637 where they seem to be saying that I shouldn't set the value using the two-way data binding this way.
I suppose I should make it read from a computed property instead and set my default from that.