JavaScript variable declaration in AngularJS

Question

I'm perusing the AngularJS source code and couldn't help but notice the following:

_angular          = window.angular,
/** @name angular */
angular           = window.angular || (window.angular = {}),

This line makes sense to me:

angular           = window.angular || (window.angular = {}),

"Use angular if already defined (from a previous inclusion?) in window, or assign window.angular to an empty object and set angular local variable to window.angular."

Some questions:

1. Why would window.angular already be defined (other than the obvious case of someone has already included it), and why would we care?
2. Why assign _angular as well as angular?

Answer 1

Going through the commit history on GitHub, this is for noConflict mode, the case where you have an old reference to a variable called angular you want to preserve.

Here is the commit that added _angular in.

The feature was then removed in this commit and the _angular reference is redundant at this point.

I'll raise an issue on GH or make a pull request shortly. Update - made a PR.