🇳🇴 NDC Oslo 2022 - Speaker Deck

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Hello, NDC Oslo 🙋 🇳🇴 🌍 WEB PERFORMANCE APIS YOU (PROBABLY) DIDN'T KNOW EXISTED • THE 28TH OF SEPTEMBER, 2022.

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WEB PERFORMANCE APIS YOU (PROBABLY) DIDN’T KNOW EXISTED MATHEUS ALBUQUERQUE

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Å I’M MATHEUS 🙋 ↝ @YTHECOMBINATOR ON THE WEB ↝ SR. SOFTWARE ENGINEER @MEDALLIA ↝ MENTOR @TECHLABS

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Disclaimers WEB PERFORMANCE APIS YOU (PROBABLY) DIDN'T KNOW EXISTED

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WEB PERFORMANCE APIS YOU (PROBABLY) DIDN'T KNOW EXISTED #1 🤯 = FURTHER DISCUSSIONS AFTER THE SESSION

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WEB PERFORMANCE APIS YOU (PROBABLY) DIDN'T KNOW EXISTED #2 60 MINUTES IS A LOT OF TIME, I KNOW… 🥱

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WEB PERFORMANCE APIS YOU (PROBABLY) DIDN'T KNOW EXISTED #2 LOT OF TIME, I KNOW… 🥱

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WEB PERFORMANCE APIS YOU (PROBABLY) DIDN'T KNOW EXISTED #3 THE IDEA BEHIND THIS SESSION IS HEAVILY INSPIRED BY ZENO'S SESSION BACK IN 2016.

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WEB PERFORMANCE APIS YOU (PROBABLY) DIDN'T KNOW EXISTED #3 SESSION BACK IN 2016.

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Why am I here? WEB PERFORMANCE APIS YOU (PROBABLY) DIDN'T KNOW EXISTED

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WEB PERFORMANCE APIS YOU (PROBABLY) DIDN’T KNOW EXISTED MATHEUS ALBUQUERQUE

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WEB PERFORMANCE STUFF YOU ALREADY KNOW MATHEUS ALBUQUERQUE

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↝ HTTP/2 (REQ/RES MULTIPLEXING; EFFICIENT COMPRESSION; REQUEST PRIORITIZATION; SERVER PUSH) ↝ COMPRESS JAVASCRIPT (E.G. WITH BROTLI) ↝ IMAGE CDNS (40–80% SAVINGS; LESS WORK WITH TRANSFORMATION, OPTIMIZATION, AND DELIVERY) YOU ALREADY KNOW…

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↝ OPTIMIZE THIRD-PARTIES (DEFER/REPLACE/ UPDATE THEM; TRY EXPERIMENTAL IDEAS) ↝ PRPL PATTERN (PUSH CRITICAL RESOURCES → RENDER THE INITIAL ROUTE ASAP → PRE-CACHE IN BACKGROUND → LAZILY LOAD OTHER STUFF) ↝ WORKERS TO OFF-LOAD THE MAIN THREAD YOU ALREADY KNOW…

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— HTTPS://WWW.PATTERNS.DEV YOU ALREADY KNOW…

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— HTTPS://WWW.PATTERNS.DEV YOU ALREADY KNOW…

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— HTTPS://WWW.PATTERNS.DEV YOU ALREADY KNOW…

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YOU ALREADY KNOW…

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#QUESTION 🤔 We're all already doing (some of) these, right?

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WEB PERFORMANCE APIS YOU (PROBABLY) DIDN'T KNOW EXISTED

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Å — APP DYNAMICS REPORT, LAST THREE MONTHS

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Å — APP DYNAMICS REPORT, LAST THREE MONTHS

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Å — APP DYNAMICS REPORT, LAST THREE MONTHS

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Å FIXING WEB PERFORMANCE

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Å FIXING WEB PERFORMANCE

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This talk presents Why am I here? Measuring Measuring (with the platform) Optimizing (with the platform) Why are we here? Closing thoughts

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This talk presents Why am I here? Measuring Measuring (with the platform) Optimizing (with the platform) Why are we here? Closing thoughts

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Measuring WEB PERFORMANCE APIS YOU (PROBABLY) DIDN'T KNOW EXISTED

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#QUESTION 🤔 What does it mean to be fast?

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#QUESTION 🤔 What does it mean to be fast? If you were to summarize web performance in one metric, what’d be your pick?

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#QUESTION 🤔 What does it mean to be fast? If you were to summarize web performance in one metric, what’d be your pick? e.g. load time, responsiveness, etc.

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WEB PERFORMANCE APIS YOU (PROBABLY) DIDN'T KNOW EXISTED If you were to summarize web performance in one metric, what’d be your pick?

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WEB PERFORMANCE APIS YOU (PROBABLY) DIDN'T KNOW EXISTED If you were to summarize web performance in one metric, what’d be your pick? 1st/2nd/3rd ANSWERS ↝ REACT BRUSSELS DISCOUNT CODE 🇧🇪 OTHERS ↝ STICKERS 💅

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WEB PERFORMANCE APIS YOU (PROBABLY) DIDN'T KNOW EXISTED

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#PROTIP💡 A lot of loading metrics don't capture user experience. We need to think about our metrics in terms of what matters.

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#QUOTE 🦄 "My app loads in n seconds…" — Front-End Engineers, ca. 2022

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#PROTIP💡 Load metrics are not a single number.

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#QUESTION 🤔 What does it mean to be fast? If you were to summarize web performance in one metric, what’d be your pick?

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WEB PERFORMANCE APIS YOU (PROBABLY) DIDN'T KNOW EXISTED If you were to summarize web performance in one metric, what’d be your pick?

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MEASURING PERCEIVED LOAD SPEED HOW QUICKLY A PAGE CAN LOAD AND RENDER ALL OF ITS VISUAL ELEMENTS TO THE SCREEN LOAD RESPONSIVENESS HOW QUICKLY A PAGE CAN LOAD/RUN ANY REQUIRED JS IN ORDER FOR COMPONENTS TO RESPOND TO USER INTERACTION RUNTIME RESPONSIVENESS AFTER THE PAGE LOAD, HOW QUICKLY CAN THE PAGE RESPOND TO USER INTERACTION? SMOOTHNESS DO TRANSITIONS & ANIMATIONS RENDER AT A CONSISTENT FRAME RATE AND FLOW FLUIDLY?

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#PROTIP💡 The only way to truly know how your site performs for your users is to actually measure its performance as those users are loading and interacting with it.

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WEB PERFORMANCE APIS YOU (PROBABLY) DIDN'T KNOW EXISTED Jean-Antoine Nollet

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↝ THE FIRST EVER RUM EXPERIMENT IN 1746 ↝ HE GATHERED ˜200 MONKS IN CIRCUMFERENCE, WIRED USING IRON, AND DISCHARGED A BATTERY THROUGH THE HUMAN CHAIN ↝ HE WAS TESTING THE LATENCY OF AN ELECTRIC SIGNAL WITH REAL USERS JEAN-ANTOINE NOLLET

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#PROTIP💡 Browsers now provide us with many apis to fetch performance metrics that help site owners make sites faster.

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WEB PERFORMANCE STUFF YOU ALREADY KNOW MATHEUS ALBUQUERQUE

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WEB PLATFORM PERF APIS I DIDN’T KNOW EXISTED MATHEUS ALBUQUERQUE

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Measuring with the platform WEB PERFORMANCE APIS YOU (PROBABLY) DIDN'T KNOW EXISTED

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MEASUREMENT APIS GENERAL STUFF DOMHighResTimeStamp, PerformanceObserver, PAGE VISIBILITY API & LAYOUT INSTABILITY API PROFILING LONG TASKS API, UserAgentSpecificMemory & JS SELF- PROFILING API TIMING USER TIMING, ELEMENT TIMING. EVENT TIMING, RESOURCE TIMING, NAVIGATION TIMING & SERVER TIMING SENSORS BATTERY STATUS & NETWORK INFORMATION

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GENERAL STUFF DOMHighResTimeStamp MICROSECOND RESOLUTION & BASED ON THE TIME AT WHICH THE USER NAVIGATED TO THE PAGE LAYOUT INSTABILITY ALL LAYOUT SHIFT EVENTS ON A PAGE PerformanceObserver SUBSCRIBE TO PERFORMANCE-RELATED EVENTS PAGE VISIBILITY KNOW WHEN A DOCUMENT BECOMES VISIBLE OR HIDDEN

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document.hidden; document.visibilityState; document.addEventListener("visibilitychange",() = > { if(document.visibilityState==="hidden"){ console.log("This window is hidden") } else{ console.log("This window is visible") } }) PAGE VISIBILITY

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↝ CANCEL NETWORK REQUESTS AND OTHER TIME- BASED EVENTS ↝ SUSPEND WEB SOCKETS AND EVENTSOURCE CONNECTIONS ↝ PAUSE VIDEOS AND CAROUSELS, IF THE USER IS NOT WATCHING THEM PAGE VISIBILITY

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↝ FETCH INCOMPLETE MEDIA TO GIVE A COMPLETELY LOADED SITE WHEN ACTIVE AGAIN ↝ DOWNLOAD THE REST OF YOUR BUNDLES USING DYNAMIC IMPORTS (AND CACHE THEIR ASSETS) ↝ MONITOR THE USER’S BEHAVIOR ↝ THROTTLE TIMERS LIKE setTimeout() PAGE VISIBILITY

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↝ SUBSCRIBE TO PERFORMANCE-RELATED EVENTS ↝ CALLBACKS ARE GENERALLY FIRED DURING IDLE PERIODS ↝ YOU TELL THE OBSERVER WHAT TYPES OF ENTRIES TO LISTEN FOR PerformanceObserver

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const observer = new PerformanceObserver((list) = > { for (const entry of list.getEntries()) { console.log(entry.toJSON()); } }); observer.observe({type: 'some-entry-type'}); PerformanceObserver

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↝ MANY WEBSITES HAVE DOM ELEMENTS SHIFTING AROUND DUE TO CONTENT LOADING ASYNCHRONOUSLY ↝ THIS API GIVES US A LIST OF ALL LAYOUT SHIFT EVENTS ON A PAGE LAYOUT INSTABILITY

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[ { "name": "", "entryType": "layout-shift", "startTime": 3087.2349999990547, "duration": 0, "value": 0.3422101449275362, "hadRecentInput": false, "lastInputTime": 0 } ] LAYOUT INSTABILITY

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WEB PERFORMANCE APIS YOU (PROBABLY) DIDN'T KNOW EXISTED

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Å LAYOUT INSTABILITY

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WEB PERFORMANCE APIS YOU (PROBABLY) DIDN'T KNOW EXISTED

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Å LAYOUT INSTABILITY

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TIMING (1st ACT) USER TIMING ALLOWS YOU TO MARK POINTS IN TIME AND THEN MEASURE THE DURATION BETWEEN THOSE MARKS. EVENT TIMING EVENT PROCESSING TIME + TIME UNTIL THE NEXT FRAME CAN BE RENDERED. THE BASIS FOR THE FID METRIC. ELEMENT TIMING MEASURE THE RENDER TIME OF SPECIFIC ELEMENTS. THE BASIS FOR THE LCP METRIC.

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/ / Record the time i m m ediately before running a task performance.mark('myTask:start'); await doMyTask(); / / Record the time i m m ediately after running a task performance.mark('myTask:end'); / / Measure the delta between the start and end of the task performance.measure('myTask', 'myTask:start', ‘myTask:end'); observer.observe({type: 'measure'}); USER TIMING

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USER TIMING

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EXAMPLE CUSTOM METRICS ↝ STYLESHEETS DONE BLOCKING ↝ SCRIPTS DONE BLOCKING ↝ FONTS LOADED ↝ TEXT DISPLAYED USER TIMING

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USER TIMING + TOOLS — "USER TIMING AND CUSTOM METRICS" BY STEVE SOUDERS

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USER TIMING + TOOLS — "USER TIMING AND CUSTOM METRICS" BY STEVE SOUDERS

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↝ ALLOWS YOU TO MEASURE THE RENDER TIME OF SPECIFIC ELEMENTS ↝ USEFUL FOR KNOWING WHEN THE LARGEST IMAGE OR TEXT BLOCK WAS PAINTED TO THE SCREEN ↝ THE BASIS FOR THE LARGEST CONTENTFUL PAINT (LCP) METRIC ELEMENT TIMING

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This is text I care about.

observer.observe({type: 'element'}); ELEMENT TIMING

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{ "name": "http://localhost:3030/public/hero.png", "id": "hero-image", "entryType": "element", "startTime": 90.68500006105751, "duration": 0, "identifier": "some-identifier", "naturalHeight": 73, "naturalWidth": 70, "intersectionRect": { "x": 253, "y": 30, "width": 71, "height": 73 } } ELEMENT TIMING

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ELEMENT TIMING + TOOLS — "ELEMENT TIMING: ONE TRUE METRIC TO RULE THEM ALL?" BY ANDY DAVIES

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ELEMENT TIMING + TOOLS

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↝ USEFUL TO MEASURE THE EVENT PROCESSING TIME AS WELL AS THE TIME UNTIL THE NEXT FRAME CAN BE RENDERED ↝ EXPOSES A NUMBER OF TIMESTAMPS IN THE EVENT LIFECYCLE ↝ THE BASIS FOR THE FIRST INPUT DELAY METRIC EVENT TIMING

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const observer = new PerformanceObserver((entryList) = > { const firstInput = entryList.getEntries()[0]; const firstInputDelay = firstInput.processingStart - firstInput.startTime; / / Measure the time it takes to run all event handlers const firstInputProcessingTime = firstInput.processingEnd - firstInput.processingStart; / / Measure the entire duration of the event const firstInputDuration = firstInput.duration; }); observer.observe({type: 'first-input'}); EVENT TIMING

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MEASURE THE LATENCY… ↝ FROM A CLICK UNTIL WE REORDER CONTENT ON A TABLE ↝ TO DRAG A SLIDER TO FILTER SOME DATA ↝ FOR A FLYOUT TO APPEAR WHEN HOVERING A MENU ITEM EVENT TIMING

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PROFILING LONG TASKS API REPORTS TASKS THAT TAKES LONGER THAN 50 MS AND IT'S THE BASIS FOR TTI AND TBT METRICS JS SELF-PROFILING API PROFILE SPECIFIC COMPLEX OPERATIONS AND IDENTIFY HOT SPOTS USING A SAMPLING PROFILER UserAgentSpecificMemory DETECT MEMORY LEAKS IN APPS THAT HANDLE A HUGE VOLUME OF DATA

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↝ REPORTS TASKS THAT TAKES LONGER THAN 50 MS ↝ USEFUL TO TRACK WHEN THE BROWSER'S MAIN THREAD IS BLOCKED ↝ THE BASIS FOR TIME TO INTERACTIVE (TTI) AND TOTAL BLOCKING TIME (TBT) METRICS LONG TASKS

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LONG TASKS

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LONG TASKS

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observer.observe({type: 'longtask'}); LONG TASKS

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observer.observe({type: 'longtask'}); { name: "same-origin-descendant", entryType: "longtask", startTime: 1023.40999995591, duration: 187.19000002602115, attribution: [ { name: "unknown", entryType: "taskattribution", startTime: 0, duration: 0, containerType: "iframe", containerSrc: "child.html", containerId: "", containerName: "child1" } ] }; LONG TASKS

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const profiler = new Profiler({ sampleInterval: 10, maxBufferSize: 10000 }); / / Do work . . . const trace = await profiler.stop(); sendProfile(trace); JS SELF-PROFILING

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↝ PROFILE SPECIFIC COMPLEX OPERATIONS ↝ PROFILE THIRD-PARTY SCRIPTS ↝ PROFILE THE ENTIRE PAGE LOAD PROCESS ↝ COMBINE WITH OTHER EVENTS/IMPORTANT METRICS, LIKE LONG TASKS OR EVENT TIMING APIS JS SELF-PROFILING

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↝ MEASURES THE MEMORY USAGE AND DETECTS MEMORY LEAKS ↝ WAITS FOR THE NEXT GC AND THEN MEASURES MEMORY IMMEDIATELY AFTER THE UNNEEDED MEMORY HAS BEEN RELEASED ↝ FORCES GC IF IT DOES NOT HAPPEN FOR 20S UserAgentSpecificMemory

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↝ FORGETTING TO UNREGISTER AN EVENT LISTENER ↝ ACCIDENTALLY CAPTURING OBJECTS FROM AN IFRAME ↝ NOT CLOSING A WORKER ↝ ACCUMULATING OBJECTS IN ARRAYS MEMORY LEAKS

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WEB PERFORMANCE APIS YOU (PROBABLY) DIDN'T KNOW EXISTED

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const obj = { a: new Array(1000), b: new Array(2000) }; setInterval(() = > { console.log(obj.a); }, 1000); MEMORY LEAKS

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performance.measureUserAgentSpecificMemory() UserAgentSpecificMemory

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↝ APPS THAT HANDLE A HUGE VOLUME OF DATA ↝ REGRESSION DETECTION DURING THE ROLLOUT OF A NEW VERSION ↝ A/B TESTING TO EVALUATE MEMORY IMPACT ↝ CORRELATING MEMORY USAGE WITH USER METRICS TO UNDERSTAND THE IMPACT OF MEMORY USAGE UserAgentSpecificMemory

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{ name: "same-origin-descendant", entryType: "longtask", startTime: 1023.40999995591, duration: 187.19000002602115, attribution: [ { name: "unknown", entryType: "taskattribution", startTime: 0, duration: 0, containerType: "iframe", containerSrc: "child.html", containerId: "", containerName: "child1" } ] } { bytes: 1000000, breakdown: [ { bytes: 1000000, attribution: [ { url: "https://example.com", scope: "Window", }, ], types: ["JS", "DOM"], }, { bytes: 0, attribution: [], types: [], }, ], } { "frames": [ { "name": "Profiler" }, { "column": 0, "line": 100, "name": "", "resourceId": 0 }, { "name": "set innerHTML" }, { "column": 10, "line": 10, "name": "A", "resourceId": 1 } { "column": 20, "line": 20, "name": "B", "resourceId": 1 } ], "resources": [ "https://example.com/page", "https://example.com/app.js", ], "samples": [ { "stackId": 0, "timestamp": 161.99500000476837 }, { "stackId": 2, "timestamp": 182.43499994277954 }, { "timestamp": 197.43499994277954 }, { "timestamp": 213.32999992370605 }, { "stackId": 3, "timestamp": 228.59999990463257 }, ], "stacks": [ { "frameId": 0 }, { "frameId": 2 }, { "frameId": 3 }, { "frameId": 4, "parentId": 2 } ] } LONG TASKS SELF-PROFILING USERAGENT MEMORY 🤯

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TIMING (2nd ACT) RESOURCE TIMING RETRIEVE AND ANALYZE DETAILED NETWORK TIMING DATA REGARDING THE LOADING SERVER TIMING COMMUNICATE PERFORMANCE METRICS ABOUT HOW TIME IS SPENT WHILE PROCESSING THE REQUEST NAVIGATION TIMING COMPLETE TIMING INFORMATION FOR NAVIGATION OF A DOCUMENT

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Å RESOURCE TIMING 🤯

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NAVIGATION TIMING

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/ / ServiceWorker startup time const workerStartupTime = entry.responseStart - entry.workerStart; / / Request time only (excluding redirects, DNS, and connection/TLS time) const requestTime = entry.responseStart - entry.requestStart; / / Response time only (download) const responseTime = entry.responseEnd - entry.responseStart; / / Request + response time const requestResponseTime = entry.responseEnd - entry.requestStart; NAVIGATION TIMING

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Server-Timing: metric1;dur=123;desc="Metric 1", metric2;dur=456;desc="Metric 2", … SERVER TIMING

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MEASURE ANY WORK THAT THE SERVER DOES TO COMPLETE A REQUEST: ↝ ROUTING/AUTHENTICATING THE REQUEST ↝ QUERYING DATABASES/API CALLS TO THIRD-PARTY SERVICES ↝ RUNNING CONTENT THROUGH TEMPLATING SYSTEMS SERVER TIMING

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Server-Timing: database;dur=123;desc="Database", templating;dur=56;desc="Template processing" SERVER TIMING

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SERVER TIMING

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WEB PERFORMANCE APIS YOU (PROBABLY) DIDN'T KNOW EXISTED

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SENSORS BATTERY STATUS INFORMATION ABOUT THE POWER SOURCE, CHARGE LEVEL, AND OTHERS NETWORK INFORMATION ADAPT THE USERS’ EXPERIENCE BASED ON THE QUALITY OF THEIR CONNECTION

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const batteryInfo = await navigator.getBattery(); batteryInfo.addEventListener("chargingchange", listener); batteryInfo.addEventListener("chargingtimechange", listener); batteryInfo.addEventListener("dischargingtimechange", listener); batteryInfo.addEventListener("levelchange", listener); BATTERY STATUS

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const networkInfo = navigator.connection; navigator.connection.addEventListener('change', onConnectionChange); NETWORK INFORMATION

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NETWORK INFORMATION const networkInfo effectiveType: "4g", rtt: 200, downlink: 1.65, saveData: false, }

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↝ SWITCH BETWEEN SERVING HIGH/LOW DEFINITION CONTENT BASED ON THE USER'S NETWORK ↝ DECIDE WHETHER TO PRELOAD RESOURCES ↝ DEFER UPLOADS/DOWNLOADS WHEN USERS ARE ON A SLOW CONNECTION ↝ ADAPT TO SITUATIONS WHEN USERS ARE OFFLINE NETWORK INFORMATION

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↝ ENABLE OFFLINE MODE IF THE NETWORK QUALITY IS NOT GOOD ENOUGH ↝ WARN USERS THAT DOING SOMETHING OVER CELLULAR COULD COST THEM MONEY ↝ USE IT IN YOUR ANALYTICS TO GATHER DATA ON YOUR USERS' NETWORK QUALITY NETWORK INFORMATION

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switch (connectionType) { case "4g": return ; case "3g": return {alt}

; default: return {alt}

; } NETWORK INFORMATION

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WEB PERFORMANCE APIS YOU (PROBABLY) DIDN'T KNOW EXISTED

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WEB PERFORMANCE APIS YOU (PROBABLY) DIDN'T KNOW EXISTED

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Improving with the platform WEB PERFORMANCE APIS YOU (PROBABLY) DIDN'T KNOW EXISTED

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WEB PERFORMANCE APIS YOU (PROBABLY) DIDN'T KNOW EXISTED Resource Hints

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↝ MANY PERFORMANCE OPTIMIZATIONS CAN BE MADE WHEN WE CAN PREDICT WHAT USERS MIGHT DO ↝ RESOURCE HINTS ARE A SIMPLE BUT EFFECTIVE WAY TO ALLOW DEVELOPERS TO HELP THE BROWSER TO STAY ONE STEP AHEAD OF THE USER AND KEEP PAGES FAST RESOURCE HINTS

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< ! - - Preconnect - - > < ! - - Preloading - - > < ! - - DNS Prefetch - - > < ! - - Prefetch - - > < ! - - Prerender - - > RESOURCE HINTS

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< ! - - Preconnect - - > < ! - - Preloading - - > < ! - - DNS Prefetch - - > < ! - - Prefetch - - > < ! - - Prerender - - > RESOURCE HINTS

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↝ IT ALLOWS THE BROWSER TO SETUP EARLY CONNECTIONS BEFORE THE REQUEST IS ACTUALLY SENT TO THE SERVER. THIS INCLUDES: • TLS NEGOTIATIONS • TCP HANDSHAKES ↝ ELIMINATES ROUNDTRIP LATENCY PRECONNECT

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100MS 200MS 300MS 400MS 500MS 600MS 700MS HTML CSS FONT 1 FONT 2 FONTS START LOADING FONTS RENDERED

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100MS 200MS 300MS 400MS 500MS 600MS 700MS HTML CSS FONT 1 FONT 2 FONTS START LOADING FONTS RENDERED FONT 1 FONT 2

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↝ IT WARNS THE BROWSER ABOUT THE DOMAINS IT’S GOING TO NEED TO LOOK UP ↝ THIS ENABLES THE IT TO DO MORE WORK IN PARALLEL, REDUCING THE OVERALL LOAD TIME ↝ USE IT WHEN YOUR PAGE USES RESOURCES FROM A DIFFERENT DOMAIN DNS PREFETCH

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↝ FETCH RESOURCES IN THE BACKGROUND (IDLE TIME) AND STORE THEM IN CACHE ↝ USE IT WHEN YOU HAVE A REASONABLE AMOUNT OF CERTAINTY ↝ THIS SHOULD BE WEIGHED AGAINST THE RISK OF WASTING RESOURCES PREFETCH

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↝ IT GOES ONE STEP FURTHER AND EXECUTES THE FILES ↝ IT DOES PRETTY MUCH ALL THE WORK REQUIRED TO DISPLAY THE PAGE, MAKING ITS LOAD FEEL INSTANTANEOUS ↝ THE GAMBLE IS EVEN GREATER HERE PRERENDER

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WEB PERFORMANCE APIS YOU (PROBABLY) DIDN'T KNOW EXISTED Priority Hints

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↝ INCREASE THE PRIORITY OF THE LCP IMAGE ↝ LOWER THE PRIORITY OF ABOVE-THE-FOLD IMAGES AND PRELOADED RESOURCES ↝ LOWER THE PRIORITY FOR NON-CRITICAL DATA FETCHES ↝ REPRIORITIZE SCRIPTS PRIORITY HINTS

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< ! - - Increase the priority of the LCP image - - >

< ! - - Lower the priority of above-the-fold images - - >

< ! - - Reprioritize scripts - - > PRIORITY HINTS

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< ! - - Increase the priority of the LCP image - - >

< ! - - Lower the priority of above-the-fold images - - >

< ! - - Reprioritize scripts - - > PRIORITY HINTS

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/ / Important validation data const user = await fetch("/user"); / / Less important content data const relatedPosts = await fetch("/posts/suggested", { priority: "low" }); PRIORITY HINTS

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/ / Important validation data const user = await fetch("/user"); / / Less important content data const relatedPosts = await fetch("/posts/suggested", { priority: "low" }); PRIORITY HINTS

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WEB PERFORMANCE APIS YOU (PROBABLY) DIDN'T KNOW EXISTED Responsive Images

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↝ IMAGES FOR DESKTOP AND TABLET CAN BE ˜2-4X LARGER THAN THE MOBILE ONES. ↝ WITH srcset, THE BROWSER WON'T DOWNLOAD THE LARGER IMAGES UNLESS THEY'RE NEEDED. THAT SAVES BANDWIDTH. RESPONSIVE IMAGES

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RESPONSIVE IMAGES

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RESPONSIVE IMAGES

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RESPONSIVE IMAGES

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WEB PERFORMANCE APIS YOU (PROBABLY) DIDN'T KNOW EXISTED Native Lazy- Loading

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NATIVE LAZY-LOADING

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NATIVE LAZY-LOADING

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WEB PERFORMANCE APIS YOU (PROBABLY) DIDN'T KNOW EXISTED

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#PROTIP 💡 Lazy-loading iframes can lead to 2-3% median data savings, 1-2% FCP reductions, and 2% FID improvements at the 95th percentile. — Chrome team’s research, 2019

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WEB PERFORMANCE APIS YOU (PROBABLY) DIDN'T KNOW EXISTED Native Scheduler

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SCHEDULING & THE WEB WE HAVE A FEW SCHEDULING PRIMITIVES: ↝ setTimeout ↝ requestAnimationFrame ↝ requestIdleCallback ↝ postMessage

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↝ EVERYONE SHOULD USE THE SAME SCHEDULER ↝ HAVING MORE THAN ONE SCHEDULER CAUSES RESOURCE FIGHTING ↝ WE HAVE TASKS INTERLEAVING WITH BROWSER WORK (RENDERING, GARBAGE COLLECTION) SCHEDULING & THE WEB

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#RANT 😡 We need better and uniform scheduling primitives for the web!

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WEB PERFORMANCE APIS YOU (PROBABLY) DIDN'T KNOW EXISTED

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NATIVE SCHEDULER ↝ A MORE ROBUST SOLUTION FOR SCHEDULING TASKS ↝ INTEGRATED DIRECTLY INTO THE EVENT LOOP ↝ CONTROL AND SCHEDULE PRIORITIZED TASKS IN A UNITED AND FLEXIBLE WAY ↝ ALIGNED WITH THE WORK OF THE REACT TEAM AND IN COOPERATION WITH GOOGLE, W3C AND OTHERS

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WEB PERFORMANCE APIS YOU (PROBABLY) DIDN'T KNOW EXISTED

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scheduler.postTask() SCHEDULE AND CONTROL PRIORITIZING TASKS. scheduler.wait() YIELD AND RESUME AFTER SOME AMOUNT OF TIME OR PERHAPS AFTER AN EVENT HAS OCCURRED. scheduler.yield() BREAK UP LONG TASKS BY YIELDING TO THE BROWSER AND CONTINUING AFTER BEING RESCHEDULED. isInputPending() DETERMINE IF THE CURRENT TASK IS BLOCKING INPUT EVENTS. NATIVE SCHEDULER

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scheduler.postTask() const promise = scheduler.postTask(myTask);

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scheduler.postTask() const promise = scheduler.postTask(myTask, { priority: "user-blocking" });

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scheduler.postTask() scheduler.postTask(() = > { console.log('NDC Oslo'); }, { delay: 10 }); scheduler.postTask(() = > { console.log('NDC Sydney'); }); scheduler.postTask(() = > { console.log('NDC Minnesota'); }); / / 'NDC Sydney' 'NDC Minnesota’ 'NDC Oslo'

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scheduler.postTask() const controller = new TaskController({ priority: "user-blocking" }); const signal = controller.signal; console.log(signal.priority); / / 'user-blocking' console.log(signal.aborted); / / 'false' scheduler.postTask(doWork, { signal }); controller.setPriority("background"); controller.abort();

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WEB PERFORMANCE APIS YOU (PROBABLY) DIDN'T KNOW EXISTED

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isInputPending() while (workQueue.length > 0) { if (navigator.scheduling.isInputPending()) { / / Stop doing work to handle any input event break; } let job = workQueue.shift(); job.execute(); }

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isInputPending() while (workQueue.length > 0) { if (navigator.scheduling.isInputPending()) { / / Stop doing work to handle any input event break; } let job = workQueue.shift(); job.execute(); }

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isInputPending() while (workQueue.length > 0) { if (navigator.scheduling.isInputPending(['mousedown', 'keydown'])) { / / Stop doing work to handle a mouse or key event break; } let job = workQueue.shift(); job.execute(); }

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WEB PERFORMANCE APIS YOU (PROBABLY) DIDN'T KNOW EXISTED

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scheduler.yield() async function doWork() { while (true) { let hasMoreWork = doSomeWork(); if (!hasMoreWork) { return; } await scheduler.yield(); } }

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async function doWork() { while (true) { let hasMoreWork = doSomeWork(); if (!hasMoreWork) { return; } if (!navigator.scheduling.isInputPending()) { continue; } await scheduler.yield(); } } scheduler.yield()

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WEB PERFORMANCE APIS YOU (PROBABLY) DIDN'T KNOW EXISTED

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scheduler.yield() async function findInFiles(query) { for (const file of files) { await yieldOrContinue("user-visible"); for (const line of file.lines) { fuzzySearchLine(line, query); } } }

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WEB PERFORMANCE APIS YOU (PROBABLY) DIDN'T KNOW EXISTED

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#QUESTION 🤔 How could we improve that?

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{result}

; }

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function* resourcefulOperation(value: number) { let newValue = String(value); while (true) { yield; for (let i = 0; i < 1000000; i++) { newValue = `${value} + ${i} = ${value + i}`; } return newValue; } } const initialValue = 0; const scheduler = new Scheduler(resourcefulOperation, initialValue); function ResourcefulComponent(props: { value: number }) { const { value } = props; const result = scheduler.performUnitOfWork(value); return

{result}

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{result}

; } PROMOTED TO A GENERATOR YIELDING EXECUTION DOING CONCURRENT TASKS

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WEB PERFORMANCE APIS YOU (PROBABLY) DIDN'T KNOW EXISTED

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enum SchedulerState { IDLE = "IDLE", PENDING = "PENDING", DONE = "DONE", } class Scheduler { state: SchedulerState; result: T; worker: (data: T) = > Generator; iterator: Generator; constructor(worker: (data: T) = > Generator, initialResult: T) { this.state = SchedulerState.IDLE; this.worker = worker; this.result = initialResult; } performUnitOfWork(data: T) { switch (this.state) { case "IDLE": this.state = SchedulerState.PENDING; this.iterator = this.worker(data); throw Promise.resolve(); case "PENDING": const { value, done } = this.iterator.next(); if (done) { this.result = value; this.state = SchedulerState.DONE; return value; } throw Promise.resolve(); case "DONE": this.state = SchedulerState.IDLE; return this.result; } } }

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↝ CSS TRICKS (E.G. font-display: swap AND will-change) ↝ IMPORT ON VISIBILITY (USING AN IntersectionObserver) ↝ SCHEDULING ALTERNATIVES WITH sendBeacon ↝ CANVAS + WORKERS = OffscreenCanvas …AND MUCH MORE!

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↝ AVOID THE INITIAL HTTP TO HTTPS REDIRECTS SO THAT PAGES LOAD FASTER USING HTTP STRICT TRANSPORT SECURITY (HSTS) ↝ SEND DATA WITHOUT EXTRA ROUND TRIPS WITH QUIC …AND MUCH MORE!

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WEB PERFORMANCE APIS YOU (PROBABLY) DIDN'T KNOW EXISTED

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SERVICES & OSS

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#PROTIP 💡 Start with observability services or libraries like web-vitals. Then create your own abstractions on top of the web (e.g. React hooks).

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Move Fast & Break Nothing ™ WEB PERFORMANCE APIS YOU (PROBABLY) DIDN'T KNOW EXISTED

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BROWSER COMPATIBILITY PERFORMANCE OBSERVER USER TIMING LONG TASKS ELEMENT TIMING RESOURCE TIMING NAVIGATION TIMING

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BROWSER COMPATIBILITY SERVER TIMING LAYOUT INSTABILITY JS SELF-PROFILING PAGE VISIBILITY BATTERY STATUS NETWORK INFORMATION

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WEB PERFORMANCE APIS YOU (PROBABLY) DIDN'T KNOW EXISTED

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MOVE FAST & BREAK NOTHING ™

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const Video = lazy(() = > import("./Video")); const Preview = lazy(() = > import("./Preview")); const networkInfo = useNetworkStatus(); const { With, Switch, Otherwise } = usePatternMatch(networkInfo); MOVE FAST & BREAK NOTHING ™

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Loading . . . }> MOVE FAST & BREAK NOTHING ™

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Why are we here? WEB PERFORMANCE APIS YOU (PROBABLY) DIDN'T KNOW EXISTED

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WEB PERFORMANCE APIS YOU (PROBABLY) DIDN'T KNOW EXISTED Browsers

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WEB PERFORMANCE APIS YOU (PROBABLY) DIDN'T KNOW EXISTED Which browsers are visiting our app? — APP DYNAMICS REPORT, LAST THREE MONTHS

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BROWSER TOTAL

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WEB PERFORMANCE APIS YOU (PROBABLY) DIDN'T KNOW EXISTED Devices & Connection

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#REALITYCHECK 😳 Phone users experience slow First Input Delay on 7x more websites. — Web Almanac By HTTP Archive, 2021

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DESKTOP PHONE 0 25 50 75 100 SLOW ( > = 250MS) AVERAGE FAST (<50 MS) FIRST INPUT DELAY

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BANDWIDTH MIX — GSM ASSOCIATION, 2022

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HTTPS://WWW.JUMIA.COM.NG HTTPS://MOBILE.TWITTER.COM — THE COST OF JAVASCRIPT IN 2019, BY ADDY OSMANI BANDWIDTH MIX

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6.07 (MBPS) 44.31 (MBPS) — THE STATE OF LTE BY OPEN SIGNAL, 2018 THE GLOBAL LTE PICTURE

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WEB PERFORMANCE APIS YOU (PROBABLY) DIDN'T KNOW EXISTED People

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THE TIME IT TAKES TO LOAD A PAGE HOW EASY IT IS TO FIND WHAT I'M LOOKING FOR HOW WELL THE SITE FITS MY SCREEN HOW SIMPLE THE SITE IS TO USE HOW ATTRACTIVE THE SITE LOOKS — SPEED MATTERS, VOL. 3 HOW IMPORTANT IS SPEED?

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#RESEARCH 📚 40% of Brits reported that they had become physically violent toward their computers. — British Psychology Society, 2009

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#RESEARCH 📚 38% of Americans with computer issues reported that they had screamed, yelled, or physically assaulted their computers. — crucial.com research, 2013

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#RESEARCH 📚 A 500ms delay resulted in up to a 26% increase in frustration and up to an 8% decrease in engagement. — Radware research, 2013

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#RESEARCH 📚 Delayed web pages caused a 38% rise in mobile users' heart rates — equivalent to the anxiety of watching a horror movie alone. — Ericsson ConsumerLab neuro research, 2015

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#RESEARCH 📚 53% of mobile users abandon sites that take over 3 seconds to load. — DoubleClick, 2020

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#PROTIP💡 People from different parts of the world have a different threshold for frustration. — UNDERSTANDING EMOTION FOR HAPPY USERS, BY PHILIP TELLIS

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— UNDERSTANDING EMOTION FOR HAPPY USERS, BY PHILIP TELLIS FRUSTATION INDEX

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WEB PERFORMANCE APIS YOU (PROBABLY) DIDN'T KNOW EXISTED Business

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↝ LONG TASKS DELAYED TTI ↝ AS FIRST-PAGE LONG TASK TIME INCREASED, OVERALL CONVERSION RATES DECREASED ↝ MOBILE HAD UP TO ˜12X LONGER LONG TASKS ↝ OLDER DEVICES COULD BE SPENDING HALF OF THEIR LOAD-TIME ON LONG TASKS BUSINESS OUTCOMES — AKAMAI AND CHROME RESEARCH, 2017

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BUSINESS OUTCOMES — AKAMAI AND CHROME RESEARCH, 2017

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↝ THE RANGE OF BROWSERS THAT PEOPLE USE IS USUALLY WIDER THAN WE THINK ↝ ACCESS TO 4G AND 5G IS STILL (VERY) LIMITED IN SOME PARTS OF THE GLOBE ↝ 4G/5G AVAILABILITY AND 4G/5G SPEED ARE DIFFERENT METRICS WHY ARE WE HERE?

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↝ ANYTHING THAT SLOWS DOWN OR PREVENTS PEOPLE FROM ACCOMPLISHING THEIR GOALS WILL CAUSE FRUSTRATION ↝ PEOPLE WILL ABANDON SITES THAT CAUSE FRUSTRATION WHY ARE WE HERE?

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WEB PERFORMANCE APIS YOU (PROBABLY) DIDN'T KNOW EXISTED Closing Notes

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WEB PERFORMANCE APIS YOU (PROBABLY) DIDN'T KNOW EXISTED ALWAYS TRY TO CORRELATE BUSINESS METRICS WITH PERFORMANCE. #1

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WEB PERFORMANCE APIS YOU (PROBABLY) DIDN'T KNOW EXISTED DON'T TAKE FAST NETWORKS, CPUS AND RAM FOR GRANTED. #2

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WEB PERFORMANCE APIS YOU (PROBABLY) DIDN'T KNOW EXISTED TEST ON REAL PHONES AND NETWORKS. #3

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WEB PERFORMANCE APIS YOU (PROBABLY) DIDN'T KNOW EXISTED AVOID THE OBSERVER EFFECT. #4

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WEB PERFORMANCE APIS YOU (PROBABLY) DIDN'T KNOW EXISTED GET RID OF THE NOISE IN YOUR METRICS. #5

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WEB PERFORMANCE APIS YOU (PROBABLY) DIDN'T KNOW EXISTED THERE'S NO SILVER BULLET. IDENTIFY YOUR CORE METRICS. #6

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WEB PERFORMANCE APIS YOU (PROBABLY) DIDN'T KNOW EXISTED "IN GOD WE TRUST. ALL OTHERS MUST BRING DATA." — W. EDWARDS DEMING #7

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