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[amp-analytics] Use IntersectionObserver to do visibility tracking #5697

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lannka opened this Issue Oct 19, 2016 · 1 comment

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lannka commented Oct 19, 2016

Comparing to the current scroll-event based approach, native IntersectionObserver provides the following benefit:

  • More performant. The current approach invokes calculation on every scroll event. InOb only invokes calculation when intersect boundary has been crossed.
  • More accurate visibility tracking. Because the current approach doesn't take DOM mutation into consideration, hence is not accurate. InOb will take care of it.
  • Work inside xorigin iframe, such as the case of amp-inabox (#5700), where we can't use the current scroll-event based approach.

Note: IntersectionObserver only fires when the intersection is crossing a list of pre-specified thresholds, hence we will not have exact value for metrics minVisiblePercentage and maxVisiblePercentage. We decided to approximate the values using thresholds of [0, 0.05, 0.1, ..., 1]. See discussion here: #5942

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lannka Dec 28, 2016

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Further clean up work is tracked separately in #6828

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lannka commented Dec 28, 2016

Further clean up work is tracked separately in #6828

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