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quotation from https://developers.google.com/gtagjs/reference/api

gtag(<command>, <command parameters>);

<command> is one of three gtag commands: config, set, or event.

but snippet provided by https://developers.google.com/analytics/devguides/collection/gtagjs/ contains such line

gtag('js', new Date());

What's her job?

4
  • 1
    I'm not sure. My guess is that the date is used as a cache busting parameter. See What is cache busting? · Curtis Timson which has a section about using dates and times. I'm not sure why you would have to pass the date into that function though. I'd think it could just instantiate a new date on its own if it needed one for cache busting. Jan 7, 2019 at 10:08
  • @StephenOstermiller, Or could it have something to do with [support.google.com/analytics/answer/6086069?hl=en] ?
    – nichijou
    Jan 7, 2019 at 14:01
  • Could be. Again, I don't know why you would have to pass the date in for that either. Jan 7, 2019 at 14:29
  • @StephenOstermiller, maybe serve as some kind of self-explanatory stuff
    – nichijou
    Jan 7, 2019 at 23:27

2 Answers 2

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It's for setting GA's cookie and reporting timezone/region/language to various functions responsible for functionality based on time...which is a lot. Most things in Google Analytics revolve around time in one way or another. For example session durations, time on page, the time of day that users visit your site, etc.

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Couldn't find more information out there but I think it could be like similar to gtm.start but for gtag. See more about gtm.start here: https://hume.dev/articles/gtm-start/ It might either be useful for tracking loading time (performance) or for serving as a seed for calculating unique ids per page load.

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