Chrome DevTools: State of the Union 2024 - Debugging React & Beyond

by Addy Osmani

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JSNATION THE QUALITY OF THE OUTCOME OFTEN DEPENDS ON QUALITY OF THE TOOLS

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JSNATION CAN AI TRANSFORM COMPLEXITY INTO CLARITY?

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GET ASSISTANCE IN DEVTOOLS WITH AI

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UNDERSTAND ERRORS IN DEVTOOLS USING AI

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ASK ABOUT SOURCES …OR NETWORK OR WEBPERF

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JSNATION WITH EXTENSIBILITY YOUR TOOLS EVOLVE AS QUICKLY AS YOU DO

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HIGHLIGHT UPDATES WHEN COMPONENTS RE-RENDER

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REACT DEVTOOLS BADGES SERVER COMPONENTS!

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SERVER LOGGING IN NEXT.JS

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TOGGLE SUSPENSE FALLBACKS WITH REACT DEVTOOLS

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REACT COMPILER SUPPORT IN DEV TOOLS

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INSPECT HOOKS WITH REACT DEVTOOLS

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CUSTOM HOOK DEBUGGING WITH USEDEBUGVALUE

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JSNATION EXPERIMENT FREELY WITHOUT TOUCHING THE ORIGINAL CODE

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“EDIT” LIVE PAGES WITH DEVTOOLS

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AUTO-FIX COLOR CONTRAST

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“EDIT” LIVE PAGES WITH OVERRIDES

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OVERRIDE THE CONTENT OF XHR AND FETCH REQUESTS

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OVERRIDE HTTP RESPONSE HEADERS!

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PASTE ENTIRE HEADER STRINGS TO OVERRIDE THEM

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DEV TOOLS TIP: HIDE CHROME EXTENSION REQUESTS

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DEVTOOLS NOW HAS HUMAN-READABLE HTTP STATUS CODES

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EMULATE A FOCUSED PAGE IN ELEMENTS > STYLES

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JSNATION LAB PERFORMANCE DATA SHOW’S WHAT’S POSSIBLE. FIELD SHOWS WHAT’S REAL.

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MONITOR LOCAL & FIELD PERFORMANCE

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RECOMMENDATIONS IN LIVE METRICS “Real users may have slower interactions due to slower CPU speeds” “Screen size can influence LCP”

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GET INSIGHTS RIGHT IN THE PERFORMANCE PANEL LCP by phase Layout shift culprits Third-parties Render blocking requests And more

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ANNOTATE + SHARE PERFORMANCE FINDINGS

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DEVTOOLS HAS A BUNDLE ANALYZER

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What is input responsiveness? FIRST INPUT DELAY TOTAL BLOCKING TIME TIME TO INTERACTIVE INP

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Click ➡ Open Menu

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Click ➡ Add to Cart

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OPTIMIZING INP FOR REACT APPS https://dub.sh/YGjr0UR

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REACT 18+ CONCURRENT RENDERING IMPACT From sync to concurrent rendering • Rendering is interruptible • Enables better prioritization of user interactions • Impact: • Desktop: 46% improvement (450ms → 240ms) • Mobile: 54% improvement (1.1s → 500ms https://dub.sh/YGjr0UR

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BREAKING UP LONG TASKS Yield to the main thread between operations https://dub.sh/YGjr0UR • Track events were causing main thread blocking • Solution: Yield to main thread between operations • Impact • Implementation using setTimeout(0) or scheduler API • 19% improvement in INP (saved ~120ms)

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REACT RE-RENDERING OPTIMIZATIONS • Simplify complex custom hooks causing re-rendering • Replace React Router APIs with window.location/history • Colocate functions within useE ff ect • Memoize selectors properly • Impact • Another 45% INP improvement Before After

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FINAL RESULTS & KEY RECOMMENDATIONS Pro fi ling with Chrome & React DevTools can help lead to signi fi cant gains • Results: • INP General: 69% improvement (850ms → 260ms) • INP Mobile: 72% improvement (1.1s → 300ms) • INP Desktop: 66% improvement (440ms → 150ms) • Key Recommendations: • Simplify abstractions (smaller hooks, colocated state) • Defer non-UI related code • Properly memoize selectors • Break up long tasks https://dub.sh/YGjr0UR

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JSNATION A SEAMLESS USER EXPERIENCE COMES FROM SWEATING THE SMALL STUFF.

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PUSH THE WEB FORWARD JSNATION

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ANIMATION INSPECTOR

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CAPTURE ANIMATIONS AND EDIT @KEYFRAMES LIVE

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NEXT.JS + VIEW TRANSITIONS Built with https://github.com/shuding/next-view-transitions