Issue 5735 - Use JS Map instead of Object for global keyByFilter in elemHide.js

# depends on https://codereview.adblockplus.org/29551635/

[sergei, 2017-09-21 12:02:10]

https://codereview.adblockplus.org/29551638/diff/29551639/lib/elemHide.js
File lib/elemHide.js (right):

https://codereview.adblockplus.org/29551638/diff/29551639/lib/elemHide.js#new...
lib/elemHide.js:35: * @type {Map.<string,string>}
Pay attention that after switching from Object to Map one can use Objects as
keys, so here it could be Map.<Filter,string>, I will measure it and if it's
better then either update this codereview or create a  new one.

[kzar, 2017-09-22 10:50:15]

https://codereview.adblockplus.org/29551638/diff/29551639/lib/elemHide.js
File lib/elemHide.js (right):

https://codereview.adblockplus.org/29551638/diff/29551639/lib/elemHide.js#new...
lib/elemHide.js:35: * @type {Map.<string,string>}
On 2017/09/21 12:02:10, sergei wrote:
> Pay attention that after switching from Object to Map one can use Objects as
> keys, so here it could be Map.<Filter,string>, I will measure it and if it's
> better then either update this codereview or create a  new one.

Yea, it looks like we only used the Filter's text as the key since we had to. I
agree using the Filter itself as the key would be nicer, please could you change
that in this review?

[Wladimir Palant, 2017-09-25 10:59:32]

https://codereview.adblockplus.org/29551638/diff/29551639/lib/elemHide.js
File lib/elemHide.js (right):

https://codereview.adblockplus.org/29551638/diff/29551639/lib/elemHide.js#new...
lib/elemHide.js:35: * @type {Map.<string,string>}
Agreed, we should use Filter objects as keys here.

[sergei, 2017-09-25 13:41:23]

https://codereview.adblockplus.org/29551638/diff/29551639/lib/elemHide.js
File lib/elemHide.js (right):

https://codereview.adblockplus.org/29551638/diff/29551639/lib/elemHide.js#new...
lib/elemHide.js:35: * @type {Map.<string,string>}
Done.

I have checked when the type of key here is string and object and there is no
visible change in the memory usage (RSS).

[Wladimir Palant, 2017-09-25 13:57:17]

https://codereview.adblockplus.org/29551638/diff/29551639/lib/elemHide.js
File lib/elemHide.js (right):

https://codereview.adblockplus.org/29551638/diff/29551639/lib/elemHide.js#new...
lib/elemHide.js:35: * @type {Map.<string,string>}
On 2017/09/25 13:41:23, sergei wrote:
> I have checked when the type of key here is string and object and there is no
> visible change in the memory usage (RSS).

A change in memory usage would be unexpected, both approaches reuse existing
objects as keys instead of copying data around. Performance might be better with
objects however because comparing them is simpler than comparing strings.

[kzar, 2017-09-25 15:21:15]

LGTM

[Wladimir Palant, 2017-09-26 11:12:14]

LGTM