Handle zero-area and display: none cases

Attempts to satsify the spec: https://www.w3.org/TR/intersection-observer/#update-intersection-observations-algo

isIntersecting, non-zero area, and display:nonen are all related, so fixing in one swoop.

Fixes:
#93
#73

Related issues:
w3c/IntersectionObserver#69
w3c/IntersectionObserver#222

Author: asakusuma

src/index.ts

@@ -3,25 +3,23 @@ Copyright 2017 LinkedIn Corp. Licensed under the Apache License,
 Version 2.0 (the "License"); you may not use this file except in
 compliance with the License. You may obtain a copy of the License
 at http://www.apache.org/licenses/LICENSE-2.0
- 
+
 Unless required by applicable law or agreed to in writing, software
 distributed under the License is distributed on an "AS IS" BASIS,
 WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 */
 
 import { SpanielIntersectionObserver, generateEntry } from './intersection-observer';
 
-import { entrySatisfiesRatio } from './utils';
-
-import { SpanielTrackedElement, SpanielObserverEntry, DOMString, DOMMargin } from './interfaces';
+import { SpanielTrackedElement, DOMMargin } from './interfaces';
 
 export { Watcher, WatcherConfig } from './watcher';
 
 import { SpanielObserver } from './spaniel-observer';
 
 import { setGlobalEngine, getGlobalEngine } from './metal/engine';
 
-import { Scheduler, getGlobalScheduler, on, off, scheduleWork, scheduleRead, Frame } from './metal/index';
+import { getGlobalScheduler, on, off, scheduleWork, scheduleRead, Frame } from './metal/index';
 
 import w from './metal/window-proxy';
 
@@ -46,13 +44,13 @@ export function queryElement(el: Element, callback: (clientRect: ClientRect, fra
 }
 
 export function elementSatisfiesRatio(
-  el: Element,
+  el: HTMLElement,
   ratio: number = 0,
   callback: (result: Boolean) => void,
   rootMargin: DOMMargin = { top: 0, bottom: 0, left: 0, right: 0 }
 ) {
   queryElement(el, (clientRect: ClientRect, frame: Frame) => {
     let entry = generateEntry(frame, clientRect, el, rootMargin);
-    callback(entrySatisfiesRatio(entry, ratio));
+    callback(entry.isIntersecting && entry.intersectionRatio >= ratio);
   });
 }

src/interfaces.ts

@@ -9,7 +9,7 @@ distributed under the License is distributed on an "AS IS" BASIS,
 WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 */
 
-export interface SpanielTrackedElement extends Element {
+export interface SpanielTrackedElement extends HTMLElement {
   __spanielId: string;
 }
 

src/intersection-observer.ts

@@ -9,7 +9,7 @@ distributed under the License is distributed on an "AS IS" BASIS,
 WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 */
 
-import { entrySatisfiesRatio } from './utils';
+import { calculateIsIntersecting } from './utils';
 
 import { Frame, QueueDOMElementInterface, DOMQueue, ElementScheduler, Engine, generateToken } from './metal/index';
 
@@ -65,7 +65,7 @@ export class SpanielIntersectionObserver implements IntersectionObserver {
   public thresholds: number[];
   private records: { [index: string]: EntryEvent };
 
-  observe(target: Element) {
+  observe(target: HTMLElement) {
     let trackedTarget = target as SpanielTrackedElement;
 
     let id = (trackedTarget.__spanielId = trackedTarget.__spanielId || generateToken());
@@ -79,7 +79,7 @@ export class SpanielIntersectionObserver implements IntersectionObserver {
     );
     return id;
   }
-  private onTick(frame: Frame, id: string, clientRect: DOMRectReadOnly, el: Element) {
+  private onTick(frame: Frame, id: string, clientRect: DOMRectReadOnly, el: SpanielTrackedElement) {
     let { numSatisfiedThresholds, entry } = this.generateEntryEvent(frame, clientRect, el);
     let record: EntryEvent =
       this.records[id] ||
@@ -88,8 +88,12 @@ export class SpanielIntersectionObserver implements IntersectionObserver {
         numSatisfiedThresholds: 0
       });
 
-    if (numSatisfiedThresholds !== record.numSatisfiedThresholds) {
+    if (
+      numSatisfiedThresholds !== record.numSatisfiedThresholds ||
+      entry.isIntersecting !== record.entry.isIntersecting
+    ) {
       record.numSatisfiedThresholds = numSatisfiedThresholds;
+      record.entry = entry;
       this.scheduler.scheduleWork(() => {
         this.callback([entry]);
       });
@@ -106,14 +110,14 @@ export class SpanielIntersectionObserver implements IntersectionObserver {
   takeRecords(): IntersectionObserverEntry[] {
     return [];
   }
-  private generateEntryEvent(frame: Frame, clientRect: DOMRectReadOnly, el: Element): EntryEvent {
+  private generateEntryEvent(frame: Frame, clientRect: DOMRectReadOnly, el: HTMLElement): EntryEvent {
     let count: number = 0;
     let entry = generateEntry(frame, clientRect, el, this.rootMarginObj);
     let ratio = entry.intersectionRatio;
 
     for (let i = 0; i < this.thresholds.length; i++) {
       let threshold = this.thresholds[i];
-      if (entrySatisfiesRatio(entry, threshold)) {
+      if (entry.intersectionRatio >= threshold) {
         count++;
       }
     }
@@ -152,7 +156,7 @@ function addRatio(entryInit: SpanielIntersectionObserverEntryInit): Intersection
     intersectionRect,
     target,
     intersectionRatio,
-    isIntersecting: intersectionRatio > 0
+    isIntersecting: calculateIsIntersecting({ intersectionRect })
   };
 }
 
@@ -182,13 +186,37 @@ export class IntersectionObserverEntry implements IntersectionObserverEntryInit
 };
 */
 
+function emptyRect(): ClientRect | DOMRect {
+  return {
+    bottom: 0,
+    height: 0,
+    left: 0,
+    right: 0,
+    top: 0,
+    width: 0,
+    x: 0,
+    y: 0
+  };
+}
+
 export function generateEntry(
   frame: Frame,
   clientRect: DOMRectReadOnly,
-  el: Element,
+  el: HTMLElement,
   rootMargin: DOMMargin
 ): IntersectionObserverEntry {
-  let { top, bottom, left, right } = clientRect;
+  if (el.style.display === 'none') {
+    return {
+      boundingClientRect: emptyRect(),
+      intersectionRatio: 0,
+      intersectionRect: emptyRect(),
+      isIntersecting: false,
+      rootBounds: emptyRect(),
+      target: el,
+      time: frame.timestamp
+    };
+  }
+  let { bottom, right } = clientRect;
   let rootBounds: ClientRect = {
     left: frame.left + rootMargin.left,
     top: frame.top + rootMargin.top,

src/native-spaniel-observer.ts

@@ -9,7 +9,7 @@ distributed under the License is distributed on an "AS IS" BASIS,
 WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 */
 
-import { entrySatisfiesRatio } from './utils';
+import { calculateIsIntersecting } from './utils';
 
 import {
   IntersectionObserverInit,
@@ -187,9 +187,10 @@ export class SpanielObserver implements SpanielObserverInterface {
         let hasTimeThreshold = !!state.threshold.time;
         let spanielEntry: SpanielObserverEntry = this.generateSpanielEntry(entry, state);
 
-        const ratioSatisfied = entrySatisfiesRatio(entry, state.threshold.ratio);
+        const ratioSatisfied = entry.intersectionRatio >= state.threshold.ratio;
+        const isIntersecting = calculateIsIntersecting(entry);
 
-        if (ratioSatisfied && !state.lastSatisfied) {
+        if (ratioSatisfied && !state.lastSatisfied && isIntersecting) {
           spanielEntry.entering = true;
           if (hasTimeThreshold) {
             state.lastVisible = time;

src/spaniel-observer.ts

@@ -9,7 +9,7 @@ distributed under the License is distributed on an "AS IS" BASIS,
 WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 */
 
-import { entrySatisfiesRatio } from './utils';
+import { calculateIsIntersecting } from './utils';
 
 import { SpanielIntersectionObserver } from './intersection-observer';
 
@@ -191,9 +191,10 @@ export class SpanielObserver implements SpanielObserverInterface {
           let hasTimeThreshold = !!state.threshold.time;
           let spanielEntry: SpanielObserverEntry = this.generateSpanielEntry(entry, state);
 
-          const ratioSatisfied = entrySatisfiesRatio(entry, state.threshold.ratio);
+          const ratioSatisfied = entry.intersectionRatio >= state.threshold.ratio;
+          const isIntersecting = calculateIsIntersecting(entry);
 
-          if (ratioSatisfied && !state.lastSatisfied) {
+          if (ratioSatisfied && !state.lastSatisfied && isIntersecting) {
             spanielEntry.entering = true;
             if (hasTimeThreshold) {
               state.lastVisible = time;

src/utils.ts

@@ -1,20 +1,7 @@
 import { SpanielClientRectInterface } from './metal/interfaces';
 
-export function entrySatisfiesRatio(entry: IntersectionObserverEntry, threshold: number) {
-  let { boundingClientRect, intersectionRatio } = entry;
-
-  // Edge case where item has no actual area
-  if (boundingClientRect.width === 0 || boundingClientRect.height === 0) {
-    let { boundingClientRect, intersectionRect } = entry;
-    return (
-      boundingClientRect.left === intersectionRect.left &&
-      boundingClientRect.top === intersectionRect.top &&
-      intersectionRect.width >= 0 &&
-      intersectionRect.height >= 0
-    );
-  } else {
-    return intersectionRatio > threshold || (intersectionRatio === 1 && threshold === 1);
-  }
+export function calculateIsIntersecting({ intersectionRect }: { intersectionRect: ClientRect }) {
+  return intersectionRect.width > 0 || intersectionRect.height > 0;
 }
 
 export function getBoundingClientRect(element: Element): SpanielClientRectInterface {

test/headless/context.js

@@ -1,6 +1,6 @@
 /*
 Copyright 2017 LinkedIn Corp. Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License.
 You may obtain a copy of the License at http://www.apache.org/licenses/LICENSE-2.0
- 
+
 Unless required by applicable law or agreed to in writing, software 
distributed under the License is distributed on an "AS IS" BASIS, 
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 */
 

test/headless/run.js

@@ -16,6 +16,7 @@ server.stdout.on('data', data => {
       '--require',
       '@babel/register',
       'test/headless/specs/**/*.js',
+      'test/headless/specs/*.js',
       '--exit',
       '--timeout',
       '5000'

test/headless/specs/intersection-observer.js

@@ -7,6 +7,12 @@ Unless required by applicable law or agreed to in writing, software
distribute
 import { assert } from 'chai';
 import { default as testModule, TestClass } from './../test-module';
 
+import constants from './../../constants.js';
+
+const {
+  time: { IMPRESSION_THRESHOLD }
+} = constants;
+
 testModule(
   'IntersectionObserver',
   class extends TestClass {
@@ -55,6 +61,63 @@ testModule(
         });
     }
 
+    ['@test observing a hidden element should fire an event with a ratio of 0']() {
+      return this.context
+        .evaluate(() => {
+          window.STATE.intersectionEvents = 0;
+          window.STATE.impressions = 0;
+          let target = (window.testTarget = document.querySelector('.tracked-item[data-id="1"]'));
+          target.style.display = 'none';
+          let observer = new spaniel.IntersectionObserver(function(entries) {
+            window.STATE.intersectionEvents++;
+
+            if (entries[0].intersectionRatio > 0) {
+              window.STATE.impressions++;
+            }
+          });
+          observer.observe(target);
+        })
+        .wait(IMPRESSION_THRESHOLD)
+        .getExecution()
+        .evaluate(function() {
+          return window.STATE;
+        })
+        .then(function({ impressions, intersectionEvents }) {
+          assert.equal(impressions, 0, 'No visible events');
+          assert.equal(intersectionEvents, 1, 'Callback fired once');
+        });
+    }
+
+    ['@test hiding an observed element should fire an event without isIntersecting']() {
+      return this.context
+        .evaluate(() => {
+          window.STATE.intersectionEvents = 0;
+          window.STATE.impressions = 0;
+          let target = (window.testTarget = document.querySelector('.tracked-item[data-id="1"]'));
+          let observer = new spaniel.IntersectionObserver(function(entries) {
+            window.STATE.intersectionEvents++;
+
+            if (entries[0].isIntersecting) {
+              window.STATE.impressions++;
+            }
+          });
+          observer.observe(target);
+        })
+        .wait(IMPRESSION_THRESHOLD)
+        .evaluate(function() {
+          window.testTarget.style.display = 'none';
+        })
+        .wait(IMPRESSION_THRESHOLD)
+        .getExecution()
+        .evaluate(function() {
+          return window.STATE;
+        })
+        .then(function({ impressions, intersectionEvents }) {
+          assert.equal(intersectionEvents, 2, 'Callback fired twice');
+          assert.equal(impressions, 1, 'One visible event');
+        });
+    }
+
     ['@test observing a non visible element should not fire']() {
       return this.context
         .evaluate(function() {