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Sep 24, 2020
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Split out algorithms from IDL #449

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86 changes: 54 additions & 32 deletions index.bs
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Original file line number Diff line number Diff line change
Expand Up @@ -230,42 +230,14 @@ interface IntersectionObserver {
: <dfn constructor lt="IntersectionObserver(callback, options)">
new IntersectionObserver(callback, options)</dfn>
::
1. Let |this| be a new {{IntersectionObserver}} object
2. Set |this|'s internal {{[[callback]]}} slot to |callback|.
3. Attempt to <a>parse a root margin</a>
from |options|.{{IntersectionObserverInit/rootMargin}}.
If a list is returned,
set |this|'s internal {{[[rootMargin]]}} slot to that.
Otherwise, <a>throw</a> a {{SyntaxError}} exception.
4. Let |thresholds| be a list equal to
|options|.{{IntersectionObserverInit/threshold}}.
5. If any value in |thresholds| is less than 0.0 or greater than
1.0, <a>throw</a> a {{RangeError}} exception.
6. Sort |thresholds| in ascending order.
7. If |thresholds| is empty, append <code>0</code> to |thresholds|.
8. The {{IntersectionObserver/thresholds}} attribute getter will return
this sorted |thresholds| list.
9. Return |this|.
Return the result of running the <a>initialize a new IntersectionObserver</a>
algorithm, providing |callback| and |options|.
: <dfn>observe(target)</dfn>
::
1. If |target| is in |this|'s internal {{[[ObservationTargets]]}} slot,
return.
2. Let |intersectionObserverRegistration| be
an {{IntersectionObserverRegistration}} record
with an {{IntersectionObserverRegistration/observer}} property set to |this|,
a {{IntersectionObserverRegistration/previousThresholdIndex}} property set to <code>-1</code>,
and a {{IntersectionObserverRegistration/previousIsIntersecting}} property set to <code>false</code>.
3. Append |intersectionObserverRegistration|
to |target|'s internal {{[[RegisteredIntersectionObservers]]}} slot.
4. Add |target| to |this|'s internal {{[[ObservationTargets]]}} slot.
5. Schedule an iteration of the <a>event loop</a>
in the {{IntersectionObserver/root}}'s <a>browsing context</a>.
Run the <a>observe a target Element</a> algorithm, providing |this| and |target|.
: <dfn>unobserve(target)</dfn>
::
1. Remove the {{IntersectionObserverRegistration}} record
whose {{IntersectionObserverRegistration/observer}} property is equal to |this|
from |target|'s internal {{[[RegisteredIntersectionObservers]]}} slot.
2. Remove |target| from |this|'s internal {{[[ObservationTargets]]}} slot.
Run the <a>unobserve a target Element</a> algorithm, providing |this| and |target|.

Note: {{MutationObserver}} does not implement {{unobserve()}}.
For {{IntersectionObserver}}, {{unobserve()}} addresses the
Expand Down Expand Up @@ -540,6 +512,56 @@ which is a list of four pixel lengths or percentages.
<h3 id='algorithms'>
Algorithms</h2>

<h4 id='initialize-new-intersection-observer'>Initialize a new IntersectionObserver</h4>

To <dfn>initialize a new IntersectionObserver</dfn>, given an {{IntersectionObserverCallback}} |callback|
and an {{IntersectionObserverInit}} dictionary |options|, run these steps:

1. Let |this| be a new {{IntersectionObserver}} object
2. Set |this|'s internal {{[[callback]]}} slot to |callback|.
3. Attempt to <a>parse a root margin</a>
from |options|.{{IntersectionObserverInit/rootMargin}}.
If a list is returned,
set |this|'s internal {{[[rootMargin]]}} slot to that.
Otherwise, <a>throw</a> a {{SyntaxError}} exception.
4. Let |thresholds| be a list equal to
|options|.{{IntersectionObserverInit/threshold}}.
5. If any value in |thresholds| is less than 0.0 or greater than
1.0, <a>throw</a> a {{RangeError}} exception.
6. Sort |thresholds| in ascending order.
7. If |thresholds| is empty, append <code>0</code> to |thresholds|.
8. The {{IntersectionObserver/thresholds}} attribute getter will return
this sorted |thresholds| list.
9. Return |this|.

<h4 id='observe-target-element'>Observe a target Element</h4>

To <dfn>observe a target Element</dfn>, given an {{IntersectionObserver}} |observer|
and an {{Element}} |target|, follow these steps:

1. If |target| is in |observer|'s internal {{[[ObservationTargets]]}} slot,
return.
2. Let |intersectionObserverRegistration| be
an {{IntersectionObserverRegistration}} record
with an {{IntersectionObserverRegistration/observer}} property set to |observer|,
a {{IntersectionObserverRegistration/previousThresholdIndex}} property set to <code>-1</code>,
and a {{IntersectionObserverRegistration/previousIsIntersecting}} property set to <code>false</code>.
3. Append |intersectionObserverRegistration|
to |target|'s internal {{[[RegisteredIntersectionObservers]]}} slot.
4. Add |target| to |observer|'s internal {{[[ObservationTargets]]}} slot.
5. Schedule an iteration of the <a>event loop</a>
in the {{IntersectionObserver/root}}'s <a>browsing context</a>.

<h4 id='unobserve-target-element'>Unobserve a target Element</h4>

To <dfn>unobserve a target Element</dfn>, given an {{IntersectionObserver}} |observer|
and an {{Element}} |target|, follow these steps:

1. Remove the {{IntersectionObserverRegistration}} record
whose {{IntersectionObserverRegistration/observer}} property is equal to |this|
from |target|'s internal {{[[RegisteredIntersectionObservers]]}} slot, if present.
2. Remove |target| from |this|'s internal {{[[ObservationTargets]]}} slot, if present

<h4 id='queue-intersection-observer-task'>
Queue an Intersection Observer Task</h4>

Expand Down