feat: More advanced YouTube pre-load decisions based on device

package.json

@@ -46,8 +46,10 @@
         "@testing-library/jest-dom": "^5.11.6",
         "@testing-library/react": "^11.2.2",
         "@types/jest": "^26.0.15",
+        "@types/lodash.debounce": "^4.0.6",
         "@types/react": "^17.0.2",
         "@types/react-dom": "^17.0.1",
+        "@types/requestidlecallback": "^0.3.4",
         "@types/youtube": "^0.0.39",
         "@typescript-eslint/eslint-plugin": "^4.0.0",
         "@typescript-eslint/parser": "^3.10.1",
@@ -68,7 +70,7 @@
         "react-dom": "^17.0.1",
         "ts-jest": "^24.3.0",
         "ts-loader": "^8.0.18",
-        "typescript": "^4.1.3",
+        "typescript": "4.1.3",
         "web-vitals": "^2.1.2"
     },
     "eslintConfig": {
@@ -140,6 +142,7 @@
         ]
     },
     "dependencies": {
+        "lodash.debounce": "^4.0.8",
         "youtube-player": "^5.5.2"
     }
 }

src/YoutubeAtom.stories.tsx

@@ -28,6 +28,7 @@ export const NoConsent = (): JSX.Element => {
                 pillar={ArticlePillar.Culture}
                 height={450}
                 width={800}
+                isMainMedia={false}
             />
         </div>
     );
@@ -53,6 +54,7 @@ export const NoOverlay = (): JSX.Element => {
                 pillar={ArticlePillar.Culture}
                 height={450}
                 width={800}
+                isMainMedia={false}
             />
         </div>
     );
@@ -87,6 +89,7 @@ export const WithOverrideImage = (): JSX.Element => {
                         ],
                     },
                 ]}
+                isMainMedia={false}
             />
         </div>
     );
@@ -138,6 +141,7 @@ export const WithPosterImage = (): JSX.Element => {
                 ]}
                 height={450}
                 width={800}
+                isMainMedia={false}
             />
         </div>
     );
@@ -200,6 +204,7 @@ export const WithOverlayAndPosterImage = (): JSX.Element => {
                 ]}
                 height={450}
                 width={800}
+                isMainMedia={false}
             />
         </div>
     );
@@ -239,8 +244,61 @@ export const GiveConsent = (): JSX.Element => {
                     ]}
                     height={450}
                     width={800}
+                    isMainMedia={false}
                 />
             </div>
         </>
     );
 };
+
+export const WhenMainMedia = (): JSX.Element => {
+    return (
+        <div
+            css={css`
+                width: 800px;
+                margin: 25px;
+            `}
+        >
+            <YoutubeAtom
+                assetId="-ZCvZmYlQD8"
+                alt=""
+                role="inline"
+                eventEmitters={[
+                    (e) => console.log(`analytics event ${e} called`),
+                ]}
+                duration={252}
+                pillar={ArticlePillar.Culture}
+                height={450}
+                width={800}
+                isMainMedia={true}
+                consentState={{}}
+                posterImage={[
+                    {
+                        srcSet: [
+                            {
+                                src:
+                                    'https://media.guim.co.uk/757dd4db5818984fd600b41cdaf687668497051d/0_0_1920_1080/1000.jpg',
+                                width: 1000,
+                            },
+                            {
+                                src:
+                                    'https://media.guim.co.uk/757dd4db5818984fd600b41cdaf687668497051d/0_0_1920_1080/500.jpg',
+                                width: 500,
+                            },
+                            {
+                                src:
+                                    'https://media.guim.co.uk/757dd4db5818984fd600b41cdaf687668497051d/0_0_1920_1080/140.jpg',
+                                width: 140,
+                            },
+                            {
+                                src:
+                                    'https://media.guim.co.uk/757dd4db5818984fd600b41cdaf687668497051d/0_0_1920_1080/1920.jpg',
+                                width: 1920,
+                            },
+                        ],
+                    },
+                ]}
+            />
+        </div>
+    );
+};

src/YoutubeAtom.tsx

@@ -14,6 +14,9 @@ import { SvgPlay } from '@guardian/source-react-components';
 import { MaintainAspectRatio } from './common/MaintainAspectRatio';
 import { Placeholder } from './common/Placeholder';
 import { formatTime } from './lib/formatTime';
+import { useHasBeenSeen } from './lib/useHasBeenSeen';
+import { useOnce } from './lib/useOnce';
+import { whenIdle } from './lib/whenIdle';
 import { Picture } from './Picture';
 import { AdTargeting, ImageSource, RoleType } from './types';
 import { ArticleTheme } from '@guardian/libs';
@@ -39,6 +42,7 @@ type Props = {
     origin?: string;
     eventEmitters: ((event: VideoEventKey) => void)[];
     pillar: ArticleTheme;
+    isMainMedia: boolean;
 };
 declare global {
     interface Window {
@@ -160,6 +164,7 @@ export const YoutubeAtom = ({
     origin,
     eventEmitters,
     pillar,
+    isMainMedia,
 }: Props): JSX.Element => {
     const [iframeSrc, setIframeSrc] = useState<string | undefined>(undefined);
     const [hasUserLaunchedPlay, setHasUserLaunchedPlay] = useState<boolean>(
@@ -168,6 +173,19 @@ export const YoutubeAtom = ({
     const [hasUserHovered, setHasUserHovered] = useState<boolean>(false);
     const player = useRef<YoutubePlayerType>();
 
+    const [hasBeenSeen, setNode] = useHasBeenSeen({
+        threshold: 0,
+        debounce: true,
+    });
+
+    const [isIdle, setIsIdle] = useState<boolean>(false);
+
+    useOnce(() => {
+        whenIdle(() => {
+            setIsIdle(true);
+        });
+    }, []);
+
     const hasOverlay = overrideImage || posterImage;
 
     /**
@@ -192,20 +210,31 @@ export const YoutubeAtom = ({
      */
     const showPlaceholder = !iframeSrc && (!hasOverlay || hasUserLaunchedPlay);
     /**
-     * Load the you tube iframe if:
-     *
-     * - We have a source string defined (i.e. We have consent)
-     *
-     * and
-     *
-     * - One of these 3 things are true
-     *      - We don't have an overlay - so we have to load the video straight away
-     *      - The user has clicked on the overlay, so load the video iframe!
-     *      - The user has moved their mouse over the overlay so lets pre load
-     *        the content
+     * Load the YouTube iframe if:
      */
-    const loadIframe =
-        iframeSrc && (!hasOverlay || hasUserHovered || hasUserLaunchedPlay);
+    let loadIframe: boolean;
+    const isMobile = /Mobi/.test(navigator.userAgent);
+    if (!iframeSrc) {
+        // Never try to load the iframe if we don't have a source value for it
+        loadIframe = false;
+    } else if (!hasOverlay) {
+        // Always load the iframe if there is no overlay
+        loadIframe = true;
+    } else if (hasUserLaunchedPlay) {
+        // The overlay has been clicked so we should load the iframe
+        loadIframe = true;
+    } else if (isMobile && isMainMedia) {
+        // We're on a mobile device and the video is the main media so load
+        // the iframe early if idle
+        loadIframe = isIdle;
+    } else if (isMobile && !isMainMedia) {
+        // We're on a mobile device and the video is in the article body so
+        // load the iframe early when visible
+        loadIframe = hasBeenSeen;
+    } else {
+        // Not on a mobile device so load early when the mouse over event is fired
+        loadIframe = hasUserHovered;
+    }
 
     useEffect(() => {
         /**
@@ -393,6 +422,7 @@ export const YoutubeAtom = ({
                                 player.current.playVideo();
                         }
                     }}
+                    ref={setNode} // Used by useHasBeenSeen
                     onMouseEnter={() => setHasUserHovered(true)}
                     css={[
                         overlayStyles,

src/lib/useHasBeenSeen.ts

@@ -0,0 +1,47 @@
+import { useEffect, useState, useRef } from 'react';
+import libDebounce from 'lodash.debounce';
+
+const useHasBeenSeen = (
+    options: IntersectionObserverInit & { debounce?: boolean },
+): [boolean, React.Dispatch<React.SetStateAction<HTMLElement | null>>] => {
+    const [hasBeenSeen, setHasBeenSeen] = useState<boolean>(false);
+    const [node, setNode] = useState<HTMLElement | null>(null);
+
+    const observer = useRef<IntersectionObserver | null>(null);
+
+    // Enabling debouncing ensures the target element intersects for at least
+    // 200ms before the callback is executed
+    const intersectionFn: IntersectionObserverCallback = ([entry]) => {
+        if (entry.isIntersecting) {
+            setHasBeenSeen(true);
+        }
+    };
+    const intersectionCallback = options.debounce
+        ? libDebounce(intersectionFn, 200)
+        : intersectionFn;
+
+    useEffect(() => {
+        if (observer.current) {
+            observer.current.disconnect();
+        }
+
+        if (window.IntersectionObserver) {
+            observer.current = new window.IntersectionObserver(
+                intersectionCallback,
+                options,
+            );
+
+            const { current: currentObserver } = observer;
+
+            if (node) {
+                currentObserver.observe(node);
+            }
+
+            return () => currentObserver.disconnect();
+        }
+    }, [node, options, intersectionCallback]);
+
+    return [hasBeenSeen, setNode];
+};
+
+export { useHasBeenSeen };

src/lib/useOnce.ts

@@ -0,0 +1,17 @@
+import { useEffect, useState } from 'react';
+
+/**
+ * Ensures that the given task is only run once and only after all items in waitFor are defined
+ * @param {Function} task - The task to execute once
+ * @param {Array} waitFor - An array of variables that must be defined before the task is executed
+ * */
+export const useOnce = (task: () => void, waitFor: unknown[]): void => {
+    const [alreadyRun, setAlreadyRun] = useState(false);
+    const isReady = waitFor.every((dep) => dep !== undefined);
+    useEffect(() => {
+        if (!alreadyRun && isReady) {
+            task();
+            setAlreadyRun(true);
+        }
+    }, [alreadyRun, isReady, task]);
+};

src/lib/whenIdle.ts

@@ -0,0 +1,21 @@
+/**
+ * whenIdle executes the given callback when the browser is 'idle'
+ *
+ * @param callback Fired when requestIdleCallback runs or, if requestIdleCallback is not available, after 300ms
+ * @param options Options for requestIdleCallback
+ * @param options.timeout How long to wait for requestIdleCallback to return, defaults to 500ms
+ */
+export const whenIdle = (
+    callback: () => void,
+    options: {
+        timeout: number;
+    } = {
+        timeout: 500,
+    },
+): void => {
+    if ('requestIdleCallback' in window) {
+        window.requestIdleCallback(callback, options);
+    } else {
+        setTimeout(callback, 300);
+    }
+};

yarn.lock

@@ -2622,6 +2622,18 @@
   dependencies:
     "@types/node" "*"
 
+"@types/lodash.debounce@^4.0.6":
+  version "4.0.6"
+  resolved "https://registry.yarnpkg.com/@types/lodash.debounce/-/lodash.debounce-4.0.6.tgz#c5a2326cd3efc46566c47e4c0aa248dc0ee57d60"
+  integrity sha512-4WTmnnhCfDvvuLMaF3KV4Qfki93KebocUF45msxhYyjMttZDQYzHkO639ohhk8+oco2cluAFL3t5+Jn4mleylQ==
+  dependencies:
+    "@types/lodash" "*"
+
+"@types/lodash@*":
+  version "4.14.177"
+  resolved "https://registry.yarnpkg.com/@types/lodash/-/lodash-4.14.177.tgz#f70c0d19c30fab101cad46b52be60363c43c4578"
+  integrity sha512-0fDwydE2clKe9MNfvXHBHF9WEahRuj+msTuQqOmAApNORFvhMYZKNGGJdCzuhheVjMps/ti0Ak/iJPACMaevvw==
+
 "@types/markdown-to-jsx@^6.11.0":
   version "6.11.3"
   resolved "https://registry.yarnpkg.com/@types/markdown-to-jsx/-/markdown-to-jsx-6.11.3.tgz#cdd1619308fecbc8be7e6a26f3751260249b020e"
@@ -2764,6 +2776,11 @@
   dependencies:
     "@types/react" "*"
 
+"@types/requestidlecallback@^0.3.4":
+  version "0.3.4"
+  resolved "https://registry.yarnpkg.com/@types/requestidlecallback/-/requestidlecallback-0.3.4.tgz#819e22b8994cf547e1f17f9cb79805a5a3bb1db5"
+  integrity sha512-aTSyiZuRemRLTQkJPb25L7A4/eR2Teo5l4yJ1V6P3+MFxEZckTDkNKNtr/V1zEOMzS6H8DgxF22U6jPAPrzQvw==
+
 "@types/responselike@*":
   version "1.0.0"
   resolved "https://registry.yarnpkg.com/@types/responselike/-/responselike-1.0.0.tgz#251f4fe7d154d2bad125abe1b429b23afd262e29"
@@ -9414,6 +9431,11 @@ lodash-es@^4.17.15:
   resolved "https://registry.yarnpkg.com/lodash-es/-/lodash-es-4.17.15.tgz#21bd96839354412f23d7a10340e5eac6ee455d78"
   integrity sha512-rlrc3yU3+JNOpZ9zj5pQtxnx2THmvRykwL4Xlxoa8I9lHBlVbbyPhgyPMioxVZ4NqyxaVVtaJnzsyOidQIhyyQ==
 
+lodash.debounce@^4.0.8:
+  version "4.0.8"
+  resolved "https://registry.yarnpkg.com/lodash.debounce/-/lodash.debounce-4.0.8.tgz#82d79bff30a67c4005ffd5e2515300ad9ca4d7af"
+  integrity sha1-gteb/zCmfEAF/9XiUVMArZyk168=
+
 lodash.isequal@^4.5.0:
   version "4.5.0"
   resolved "https://registry.yarnpkg.com/lodash.isequal/-/lodash.isequal-4.5.0.tgz#415c4478f2bcc30120c22ce10ed3226f7d3e18e0"
@@ -13471,7 +13493,7 @@ typedarray@^0.0.6:
   resolved "https://registry.yarnpkg.com/typedarray/-/typedarray-0.0.6.tgz#867ac74e3864187b1d3d47d996a78ec5c8830777"
   integrity sha1-hnrHTjhkGHsdPUfZlqeOxciDB3c=
 
-typescript@^4.1.3:
+[email protected]:
   version "4.1.3"
   resolved "https://registry.yarnpkg.com/typescript/-/typescript-4.1.3.tgz#519d582bd94cba0cf8934c7d8e8467e473f53bb7"
   integrity sha512-B3ZIOf1IKeH2ixgHhj6la6xdwR9QrLC5d1VKeCSY4tvkqhF2eqd9O7txNlS0PO3GrBAFIdr3L1ndNwteUbZLYg==