Add comment about combined _.defaults and _.extend

[unclechu]

No description provided.

[jridgewell]

Please undo changes to everything but backbone.js. All of the others will be built later.

[jridgewell]

Let's link to #3842.

[captbaritone]

Rather than "makes sense" can you explain the behavior that it actually avoids?

[unclechu]

@jridgewell it's done. Is it okay that I made this revert commit? I mean if you do squash merge at the end it wont matter.

[jridgewell]

No, we can squash merge it. Still need the link to #3842. And someone else should look over the wording. @captbaritone? 😉

[unclechu]

@jridgewell

Still need the link to #3842

Do you mean I should add #3842 to the commit message?

[jridgewell]

To the comment, not the commit message.

[captbaritone]

You can just use GitHub's issue shorthand #1234. You could use this as a model: https://github.com/jashkenas/backbone/blob/master/backbone.js#L1158-L1159

[unclechu]

@jrburke how about now?

[captbaritone]

Rather than "makes sense" can you explain the behavior that it actually avoids?

[unclechu]

@captbaritone I added line about it helps to avoid conflicts with Object.prototype properties.

[captbaritone]

I'm not familiar with this issue, and those who are reading this comment probably won't be either. In what way does it "make sense"? Does it preserve attributes which have been explicitly set to undefined? Does it overwrite them?

[jridgewell]

It has two steps.

1. We have to create an object that contains all properties, attrs taking precedence over defaults. We clobber prototype inheritance here on purpose.
   • _.extend({}, defaults, attrs)
2. Anything in Step 1 that is undefined should be overridden with its defaults value. Since we clobbered prototype inheritance, we know for certain that if something is undefined, it was set specifically to undefined in attrs. (Or, if it was set in defaults, it will still be undefined after this step)
   • _.defaults(_, defaults)

[jgonggrijp]

Superseded by #4267.