Fixes #251 - Output of render should be Promise compatible.

[austinkelleher]

No description provided.

[coveralls]

Coverage increased (+0.03%) to 71.587% when pulling 0310d77 on austinkelleher:251-render-promise into da11d73 on marko-js:master.

[coveralls]

Coverage increased (+0.03%) to 71.587% when pulling beb8652 on austinkelleher:251-render-promise into da11d73 on marko-js:master.

[coveralls]

Coverage increased (+0.03%) to 71.494% when pulling 41fbe7a on austinkelleher:251-render-promise into abe0e2d on marko-js:master.

[coveralls]

Coverage increased (+0.03%) to 71.494% when pulling 41fbe7a on austinkelleher:251-render-promise into abe0e2d on marko-js:master.

[patrick-steele-idem]

If out.error() is called the finish event is still emitted. That would result in both reject and resolve being called. I'm not sure what the Promise spec says should happen when that occurs, but we should probably add code to make sure that resolve is not called when reject is called. Do you mind investigating that?

[Hesulan]

The Promises/A+ specification requires that a Promise instance must only ever handle the very first call to either resolve or reject, and ignore all further attempts at either. So as long as the correct one is called first it doesn't matter what happens after, the resolved/rejected Promise instance becomes immutable.

[Hesulan]

That being said, do be aware that a fulfilled Promise exhibits shallow immutability; the resolved/rejected value is effectively a const in that you cannot replace it, but you can still modify the result's properties. And since calling resolve or reject doesn't cause the function to exit, it's entirely possible to accidentally mutate the result.

[patrick-steele-idem]

Aren't you missing an out.end()?