fix memory leak in tooltip $element

[gregsheremeta]

Fixes #17973

[cvrebert]

@twbs-savage Retry

[twbs-savage]

Tests passed. Automated cross-browser testing via Sauce Labs and Travis CI shows that the JavaScript changes in this pull request are: CONFIRMED

Commit: a9efd66
Build details: https://travis-ci.org/twbs-savage/bootstrap/builds/120165154

(Please note that this is a fully automated comment.)

[XhmikosR]

@cvrebert: I think this looks good. Can we merge or is there something else?

[cvrebert]

@XhmikosR I just wasn't sure (without taking time to trace thru the flow) what situation makes the if necessary.

[gregsheremeta]

I'm not sure about the "if" either. The fix seemed to work without that extra "if" in our project, but according to #16451, some people need the extra "if". So I added it in there. It's just extra safety -- I see no harm in leaving it.

[cvrebert]

Guess we should merge and add a TODO to revisit the "if" later.

[XhmikosR]

@gregsheremeta: can you add the comment?

[cvrebert]

Merged as f01f3e5. (Rebased to add the comment in.)

[cvrebert]

@gregsheremeta Thanks!

[cvrebert]

Bookkeeping note: No corresponding patch appears to be required for v4, since it already nullifies the element instance variable upon tooltip destruction:

bootstrap/js/src/tooltip.js

Line 237 in 14c7ba9

this.element = null

[kntmrkm]

When release v3.3.7?

[cvrebert]

Some time in the next few weeks, most likely. As always, no absolute guarantee though.

[Herst]

The TODO comment is part of the release now.

[cvrebert]

That's fine.

[natalan]

It looks like this PR is a root cause for #20511

[gregsheremeta]

Probably want to add that "if" back in then