[dchest]

2. A library like jQuery is so popular, and is so often served from googles CDN, that chances are a user already has it in their local cache from when they downloaded it on some other site.

Which of these versions do you have cached?

3.2.1, 3.2.0, 3.1.1, 3.1.0, 3.0.0, 2.2.4, 2.2.3, 2.2.2, 2.2.1, 2.2.0, 2.1.4, 2.1.3, 2.1.1, 2.1.0, 2.0.3, 2.0.2, 2.0.1, 2.0.0, 1.12.4, 1.12.3, 1.12.2, 1.12.1, 1.12.0, 1.11.3, 1.11.2, 1.11.1, 1.11.0, 1.10.2, 1.10.1, 1.10.0, 1.9.1, 1.9.0, 1.8.3, 1.8.2, 1.8.1, 1.8.0, 1.7.2, 1.7.1, 1.7.0, 1.6.4, 1.6.3, 1.6.2, 1.6.1, 1.6.0, 1.5.2, 1.5.1, 1.5.0, 1.4.4, 1.4.3, 1.4.2, 1.4.1, 1.4.0, 1.3.2, 1.3.1, 1.3.0, 1.2.6, 1.2.3

[castis]

Asking an annoyed rhetorical question doesn't seem productive to the point you're trying to make here.

As an actual answer, it would be variable proportional to the size of the window between releases mentioned here: https://en.wikipedia.org/wiki/JQuery#Release_history

I'm sure a fair amount of people serve jQuery from a local storage. The usefulness that the user might already have it cached is a non-zero point, no matter how insignificant you may think it is.

[adventured]

Just two versions of jQuery, 1.12 and 1.11, represent approximately half of all jQuery versions in use. The top four most common versions (1.12, 1.11, 1.7, 1.8) represent close to 3/4 of all versions of jQuery in use. Version 3.x and 2.x are hardly being used by comparison to those.

That narrows your suggested problem down dramatically.

[kerkeslager]

How many do you need to make this worthwhile?

The ratio of cost of storing a library versus the cost of GETing a library is very low, so the chances of already having a library cached can be very low for the EV to be worthwhile.

Weighing that against the chance of downtime is a bit more complicated, admittedly.

[nix0n]

Looking at just minified versions from googleapis.com, I have 1.12.4, 2.2.4, 1.8.2, 1.10.2, 1.8.1, 1.9.1, and 2.1.1