Changes between Initial Version and Version 1 of IntersectionObserverNotes


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Timestamp:
Oct 12, 2018 5:29:43 PM (4 years ago)
Author:
Jon Davis
Comment:

Notes from 2018 WebKit Contributors Meeting

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  • IntersectionObserverNotes

    v1 v1  
     1= IntersectionObserver =
     2''by Ali Juma (ajuma@chromium.org)''
     3
     4- Goal: find out if an element is visible
     5    - Fully visible?
     6    - Partially visible?
     7    - Entirely offscreen?
     8    - Sites do this with JS with bounding boxes over and over again
     9- API Overview
     10    - var observer = new InstesectionObserver(callback, options);
     11    - Options:
     12        - root: Interseection with respect to an element or if null the viewport
     13        - threshold: what fraction of intersection triggers notfication
     14    - `observer.observe(target)`
     15- Implementation Challenges
     16    - Lifetime management
     17        - The observer and its callback need to live as long as there are targets to observe.
     18            - Even if the observer no longer has any JS references
     19        - The callback will keep the document alive.
     20            - It’s easy to accidentally keep the document alive indefinitely
     21    - Lack of Event Loop support
     22        - HTML EventLoop
     23            - https://webkit.org/b/160711
     24            - https://html.spec.whatwg.org/multipage/webappapis.html#processing-model-8
     25        - Blink and Gecko schedule rAF in-sync with “updating the rendering” (that is, producing a frame)
     26            - Any setTimeout call during rAF is guaranteed to fire after style/layout/paint for producing a frame
     27        - IntersectionObserver WPTs depend on this model
     28            - So do other WPTs
     29