Binding to an Observe.compute value is broken

[ccummings]

var person = new can.Observe({
    name: 'Jeeves'
});
var name = person.compute('name');
name.bind('change', function(ev, newVal, oldVal) {
    ...
});
name('Alfred');

The change handler in this example will be called twice. Once with the newVal as Alfred and a second time with newVal as the Observe instance (person).

Here's how this happens:

When the name compute is updated, we end up in compute.js and run the set function which is defined here in observe.js. This calls attr which fires a change event with newVal === 'Alfred'.

setVal is now the Observe instance since attr returns the Observe, so when the execution reaches here, a change event is triggered with newVal set to the Observe instance.

This code was added by @justinbmeyer here to extend can.compute.

[ccummings]

Seems this issue is a bit more serious than I first thought. It's not just a duplicate event that is emitted, the compute you get from Observe.compute will have its value changed to the Observe If you bind to the change event. So in the example above adding this:

setTimeout(function() {
    console.log(name())
}, 2000);

Would log the Observe because the compute has been set to the Observe instance.

[justinbmeyer]

Can you add a test and I will fix it tonight.

Sent from my iPhone

On Apr 30, 2013, at 11:24 AM, Curtis Cummings notifications@github.com wrote:

Seems this issue is a bit more serious than I first thought. It's not just a duplicate event that is emitted, the compute you get from Observe.compute will have its value changed to the Observe If you bind to the change event. So in the example above adding this:

setTimeout(function() {
console.log(name())
}, 2000);
Would log the Observe because the compute has been set to the Observe instance.

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Reply to this email directly or view it on GitHub.

[justinbmeyer]

The test seems to pass for me.