Assign extendOwn

[jridgewell]

“assign” is an ES6 standard, and naming should match it. Any dev who remotely follows ES will immediately recognize and understand what it does.

Aliases _.assign to _.extendOwn, for 1.8.0 compatibility.

Re: #2061, 4f771e0

[jashkenas]

Whoa there folks. extendOwn is a nicer name alongside extend. We can add an assign alias — but let's use extendOwn as the primary documented name, and internally.

[jridgewell]

let's use extendOwn as the primary documented name, and internally.

I strongly disagree. I'm not sure why we're actively discouraging ES6 compatibility, but keeping the two in sync is an awesome win.

[jashkenas]

ES6 is going to very soon — at least for simple things like assign — be viable. If you want to use Object.assign, just use it. If we can improve on it, let's improve on it. One of the important areas where we can improve on things is naming — a more internally consistent Underscore API is nicer than a franken-Under-ES6-score one.

[jamiebuilds]

The ideal API in my opinion would be for _.assign to behave like Object.assign and for _.extend to be an alias of _.assign. I don't see a need for the _.keysIn version of an assign method (other than for compatibility).