can.view.render update is sometimes `undefined`

[amcdnl]

The can.view.render class sometimes throws an Uncaught TypeError: undefined is not a function error because the update function is undefined at the call time.

See : https://github.com/bitovi/canjs/blob/master/view/render.js#L227

I propose we add change it to be update && update(newVal, oldVal)

See: http://screencast.com/t/jauYywxJSV

[ccummings]

The binder is called is called right away and if something updates the value before hookups are run, update will be undefined. This typically happens when a value used in live binding is updated inside of a can.view call, which is a bad thing to do.

A nicer fix is to assign a function to update at https://github.com/bitovi/canjs/blob/master/view/render.js#L261 that updates binding.value to newValue and console.warns that the developer might be shooting themselves in the foot.

This should make things work most of the time.

[daffl]

That sounds good. This issue keeps coming (e.g. #218) up so fixing it would be very helpful.

[amcdnl]

I like that ...

[wclr]

That is an old problem that happens sometimes "unexpectedly" is not resolved, and I always have to patch render.js each time I update.

[ccummings]

Looks like the incremental live lists update in #362 has fixed this issue.