Can you use observes() with {{yield}} - ember.js

Question

I would like to define a function like this (in a component in this case):
doSomething: function() {
// do something
}.observes('yield')
Where the component handlebars file could basically be:
...
{{yield}}
...
Will this do what I want? That is, when the yield value changes, will the doSomething() function be called?

Answer 1

U should use a parameter not the yield content for this! Like:
call this from the template:
{{tool-tip value=myValue"}}
and the controller:
myValue: function() {
return 'Hi %#, welcome to %#'.fmt(this.get('val1'), this.get('val2'));
}.property('val1', 'val2');
instead of the solution that u probably wanted to use:
{{tool-tip}}
Hi {{val1}}, welcome to {{val2}}
{{tool-tip}}
Let me explain u the problems with your idea:
what u have there where the {{yield}} is, is a template. U could observe the template, but the template itself never changes. The template is a compiled handlebars template!
So there is not even the string Hi {{val1}}, welcome to {{val2}} anymore, but there is a compiled version from this. So a javascript function that will produce Hi Krutius, welcome to StackOverflow if u call it with the JSON { val1: "Krutius", val2: "StackOverflow" }.
U see, this function will always be the same!
So you have two problems:
The first is to get resulting HTML that u need to insert into the title attribute of your tooltip containing thing, or to give to the tooltip() function as the template property. This is tricky. A working solution is to still use the {{yield}} in a hidden tag, grab the html and put it into your tooltip. This will work (as long the values don't change) but is definitely a dirty solution. I think u maybe have already done this, and thats why you want to observe {{yield}}.
But its important to know that the view won't rerender! For each value there is a view created and some strange <script> tags inserted into the DOM, and then a observer is attached to that single value, and when the value changes the specific place in the DOM can be found due the <script> tags and the value will be updated.
This behavior will change in the future when HTMLBars will come up. So you can't relay on it. Maybe a better working way is to call the handlebars function yourself to get the html.
But u still have another problem. When will the result of the handlebars function change? For that you would need to know what property the generated handlebars function requires. You probably could do this by analysing it, but maybe the function is different with HTMLBars? And it would need a lot of hacking into the internal ways of ember rendering the HTML!
So, over all, just don't do it. Solve it by giving a single value to the component and render the HTML for this value yourself!