I'm AFK so I can't test this and submit a PR, but overall is fairly trivial...

The now variable here isn't being used in logPageView(), so it can be removed:

now = new Date(),

• https://github.com/piwik/piwik/blob/master/js/piwik.js#L3267

I suggest getting rid of this workaround:

Date.prototype.getTimeAlias = Date.prototype.getTime;

• https://github.com/piwik/piwik/blob/master/js/piwik.js#L5488

and change the many occurrences of something = new Date() ... something.getTime() to +new Date (the '+' casts the object to an integer, thus yielding the time in milliseconds).

It's been 4 years, I recommend removing the JSON polyfill as native browser support has improved (and this line means it can no longer polyfill broken JSON implementations):

JSON2 = window.JSON || {};

• https://github.com/piwik/piwik/blob/master/js/piwik.js#L50

Wrap utf8_encode and sha1 into a polyfill for crypto.subtle.digest.

• https://developer.mozilla.org/en-US/docs/Web/API/SubtleCrypto/digest