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You can\nopt-out of state updates for a part of the React tree by using\n`,(0,n.jsx)(e.a,{href:\"https://react.dev/reference/react/memo\",children:(0,n.jsx)(e.code,{children:\"memo\"})}),\".\"]}),`\n`,(0,n.jsxs)(e.p,{children:[`I want to emphasize that I've seen many projects make the mistake of using these\nutilities as band-aids over more problematic performance problems in their apps.\nPlease read more about this in my blog post:\n`,(0,n.jsx)(e.a,{href:\"https://kentcdodds.com/blog/fix-the-slow-render-before-you-fix-the-re-render\",children:\"Fix the slow render before you fix the rerender\"}),\".\"]}),`\n`,(0,n.jsxs)(e.p,{children:[`Let's look at an example to learn how this works. You can pull this example up\nat `,(0,n.jsx)(\"a\",{target:\"_blank\",href:\"/app/example.unnecessary-rerenders/\",children:\"/app/example.unnecessary-rerenders\"}),`\n(and feel free to play with it in `,(0,n.jsx)(e.code,{children:\"examples/unnecessary-rerenders\"}),`). Pull this\nup and profile it with the React DevTools.`]}),`\n`,(0,n.jsx)(e.p,{children:\"Here's the implementation:\"}),`\n`,(0,n.jsx)(e.pre,{\"data-line-numbers\":\"true\",\"data-lang\":\"tsx\",style:{color:\"var(--base05)\",backgroundColor:\"var(--base00)\"},children:(0,n.jsxs)(e.code,{children:[(0,n.jsxs)(e.span,{className:\"codeblock-line\",\"data-line-number\":\"1\",children:[(0,n.jsx)(e.span,{style:{color:\"var(--base0D)\"},children:\"function\"}),\" 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But the\n`,(0,n.jsx)(e.code,{children:\"\"}),` is also rerendered. If you have\n`,(0,n.jsx)(e.code,{children:\"Record why each component rendered while profiling.\"}),` enabled in React DevTools,\nthen you'll see that under \"Why did this render?\" it says \"The parent component\nrendered.\"`]}),`\n`,(0,n.jsx)(e.p,{children:`React does this because it has no way of knowing whether the NameInput will need\nto return different React elements based on the state change of its parent. In\nour case there were no changes necessary, so React didn't bother updating the\nDOM. This is what's called an \"unnecessary rerender\" and if that\nrender/reconciliation process is expensive, then it can be worthwhile to prevent\nit.`}),`\n`,(0,n.jsxs)(e.p,{children:[`Using one of the bail-out APIs, you can instruct React when to rerender.\nThe only relevant API these days is `,(0,n.jsx)(e.code,{children:\"memo\"}),`. What happens is that React will\ncompare the previous props with the new props and if they're the same, then\nReact will not call the component function and will not update the DOM.`]}),`\n`,(0,n.jsx)(e.p,{children:\"So here's how we can improve our example:\"}),`\n`,(0,n.jsx)(e.pre,{\"data-line-numbers\":\"true\",\"data-lang\":\"tsx\",style:{color:\"var(--base05)\",backgroundColor:\"var(--base00)\"},children:(0,n.jsxs)(e.code,{children:[(0,n.jsxs)(e.span,{className:\"codeblock-line\",\"data-line-number\":\"1\",children:[(0,n.jsx)(e.span,{style:{color:\"var(--base0E)\"},children:\"import\"}),\" { \",(0,n.jsx)(e.span,{style:{color:\"var(--base08)\"},children:\"memo\"}),\" } \",(0,n.jsx)(e.span,{style:{color:\"var(--base0E)\"},children:\"from\"}),\" 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\",(0,n.jsx)(e.span,{style:{color:\"var(--base0D)\"},children:\"=>\"}),\" \",(0,n.jsx)(e.span,{style:{color:\"var(--base0D)\"},children:\"onNameChange\"}),\"(\",(0,n.jsx)(e.span,{style:{color:\"var(--base08)\"},children:\"e\"}),\".\",(0,n.jsx)(e.span,{style:{color:\"var(--base0D)\"},children:\"currentTarget\"}),\".\",(0,n.jsx)(e.span,{style:{color:\"var(--base08)\"},children:\"value\"}),\")\",(0,n.jsx)(e.span,{style:{color:\"var(--base0F)\"},children:\"}\"}),`\n`]}),(0,n.jsxs)(e.span,{className:\"codeblock-line\",\"data-line-number\":\"26\",children:[\"\t\t\t/>\",`\n`]}),(0,n.jsxs)(e.span,{className:\"codeblock-line\",\"data-line-number\":\"27\",children:[\"\t\t\",`\n`]}),(0,n.jsxs)(e.span,{className:\"codeblock-line\",\"data-line-number\":\"28\",children:[\"\t)\",`\n`]}),(0,n.jsxs)(e.span,{className:\"codeblock-line\",\"data-line-number\":\"29\",children:[\"})\",`\n`]}),(0,n.jsx)(e.span,{className:\"codeblock-line\",\"data-line-number\":\"30\",children:`\n`}),(0,n.jsxs)(e.span,{className:\"codeblock-line\",\"data-line-number\":\"31\",children:[(0,n.jsx)(e.span,{style:{color:\"var(--base03)\"},children:\"// etc... no other changes necessary\"}),`\n`]})]})}),`\n`,(0,n.jsxs)(e.p,{children:[\"The only change there was to wrap the \",(0,n.jsx)(e.code,{children:\"NameInput\"}),\" component in react's \",(0,n.jsx)(e.code,{children:\"memo\"}),`\nutility.`]}),`\n`,(0,n.jsxs)(e.p,{children:[\"If you try that out, then you'll notice the \",(0,n.jsx)(e.code,{children:\"\"}),` no longer rerenders\nwhen you click on the counter button, saving React the work of having to call\nthe `,(0,n.jsx)(e.code,{children:\"NameInput\"}),` function and compare the previous react elements with the new\nones.`]}),`\n`,(0,n.jsxs)(e.p,{children:[`Again, I want to mention that people can make the mistake of wrapping\n`,(0,n.jsx)(e.em,{children:\"everything\"}),\" in \",(0,n.jsx)(e.code,{children:\"memo\"}),` which can actually slow down your app in some cases and\nin all cases it makes your code more complex.`]}),`\n`,(0,n.jsxs)(e.p,{children:[\"In fact, why don't you try wrapping the \",(0,n.jsx)(e.code,{children:\"CountButton\"}),\" in \",(0,n.jsx)(e.code,{children:\"memo\"}),` and see what\nhappens. You'll notice that it doesn't work.`]}),`\n`,(0,n.jsxs)(e.p,{children:[\"This is because its parent is passing \",(0,n.jsx)(e.code,{children:\"increment\"}),` and that function is new every\nrender (as it's defined in the `,(0,n.jsx)(e.code,{children:\"App\"}),\"). Because \",(0,n.jsx)(e.code,{children:\"memo\"}),` relies on the same props\neach call to prevent unnecessary renders, we're not getting any benefit! If we\nreally wanted to take advantage of `,(0,n.jsx)(e.code,{children:\"memo\"}),\" here, we'd have to wrap \",(0,n.jsx)(e.code,{children:\"increment\"}),` in\n`,(0,n.jsx)(e.code,{children:\"useCallback\"}),\". Feel free to try that if you'd like.\"]}),`\n`,(0,n.jsxs)(e.p,{children:[\"It's much better to use \",(0,n.jsx)(e.code,{children:\"memo\"}),` more intentionally and further, there are other\nthings you can do to reduce the amount of unnecessary rerenders throughout your\napplication (some of which we've done already).`]})]})}function h(a={}){let{wrapper:e}=a.components||{};return e?(0,n.jsx)(e,{...a,children:(0,n.jsx)(d,{...a})}):d(a)}function w(a,e){throw new Error(\"Expected \"+(e?\"component\":\"object\")+\" `\"+a+\"` to be defined: you likely forgot to import, pass, or provide it.\")}return f(D);})();\n;return Component;","finishedCode","var Component=(()=>{var f=Object.create;var i=Object.defineProperty;var u=Object.getOwnPropertyDescriptor;var h=Object.getOwnPropertyNames;var x=Object.getPrototypeOf,l=Object.prototype.hasOwnProperty;var g=(e,n)=>()=>(n||e((n={exports:{}}).exports,n),n.exports),j=(e,n)=>{for(var o in n)i(e,o,{get:n[o],enumerable:!0})},a=(e,n,o,c)=>{if(n&&typeof n==\"object\"||typeof n==\"function\")for(let r of h(n))!l.call(e,r)&&r!==o&&i(e,r,{get:()=>n[r],enumerable:!(c=u(n,r))||c.enumerable});return e};var _=(e,n,o)=>(o=e!=null?f(x(e)):{},a(n||!e||!e.__esModule?i(o,\"default\",{value:e,enumerable:!0}):o,e)),w=e=>a(i({},\"__esModule\",{value:!0}),e);var p=g((E,d)=>{d.exports=_jsx_runtime});var k={};j(k,{default:()=>m,frontmatter:()=>y});var t=_(p()),y=void 0;function s(e){let n={h1:\"h1\",p:\"p\",...e.components},{EpicVideo:o}=n;return o||b(\"EpicVideo\",!0),(0,t.jsxs)(t.Fragment,{children:[(0,t.jsx)(n.h1,{children:\"Optimize Rendering\"}),`\n`,(0,t.jsx)(o,{url:\"https://www.epicreact.dev/workshops/react-performance/dad-joke-break-optimize-rendering\"}),`\n`,(0,t.jsx)(n.p,{children:`\\u{1F468}\\u200D\\u{1F4BC} When you find yourself rendering a ton of the same component, optimizing that\none component can have an outsized impact on performance. Good job!`})]})}function m(e={}){let{wrapper:n}=e.components||{};return n?(0,t.jsx)(n,{...e,children:(0,t.jsx)(s,{...e})}):s(e)}function b(e,n){throw new Error(\"Expected \"+(n?\"component\":\"object\")+\" `\"+e+\"` to be defined: you likely forgot to import, pass, or provide it.\")}return w(k);})();\n;return Component;","instructionsEpicVideoEmbeds",[521],"https://www.epicreact.dev/workshops/react-performance/intro-to-optimize-rendering","finishedEpicVideoEmbeds",[524],"https://www.epicreact.dev/workshops/react-performance/dad-joke-break-optimize-rendering",[526,554,573],{"_322":311,"_320":527,"_336":544},{"_20":143,"_186":471,"_513":528,"_22":144,"_24":145,"_515":529,"_530":531,"_533":534,"_537":538,"_541":542,"_310":341,"_322":311,"_9":320,"_543":147},"01.problem.memo","var Component=(()=>{var m=Object.create;var i=Object.defineProperty;var p=Object.getOwnPropertyDescriptor;var u=Object.getOwnPropertyNames;var f=Object.getPrototypeOf,w=Object.prototype.hasOwnProperty;var b=(t,e)=>()=>(e||t((e={exports:{}}).exports,e),e.exports),x=(t,e)=>{for(var o in e)i(t,o,{get:e[o],enumerable:!0})},s=(t,e,o,c)=>{if(e&&typeof e==\"object\"||typeof e==\"function\")for(let r of u(e))!w.call(t,r)&&r!==o&&i(t,r,{get:()=>e[r],enumerable:!(c=p(e,r))||c.enumerable});return t};var y=(t,e,o)=>(o=t!=null?m(f(t)):{},s(e||!t||!t.__esModule?i(o,\"default\",{value:t,enumerable:!0}):o,t)),g=t=>s(i({},\"__esModule\",{value:!0}),t);var h=b((M,a)=>{a.exports=_jsx_runtime});var k={};x(k,{default:()=>l,frontmatter:()=>v});var n=y(h()),v=void 0;function d(t){let e={code:\"code\",h1:\"h1\",p:\"p\",...t.components},{EpicVideo:o}=e;return o||j(\"EpicVideo\",!0),(0,n.jsxs)(n.Fragment,{children:[(0,n.jsx)(e.h1,{children:\"Component Memoization\"}),`\n`,(0,n.jsx)(o,{url:\"https://www.epicreact.dev/workshops/react-performance/component-memoization\"}),`\n`,(0,n.jsx)(e.p,{children:\"\\u{1F468}\\u200D\\u{1F4BC} We've got a problem. Here's how you reproduce it in our component.\"}),`\n`,(0,n.jsxs)(e.p,{children:[`In this exercise, pull up the React DevTools Profiler and start a recording.\nObserve when you click the \"force rerender\" button, the `,(0,n.jsx)(e.code,{children:\"CityChooser\"}),` and\n`,(0,n.jsx)(e.code,{children:\"ListItem\"}),` components are rerendered even though no DOM updates were needed.\nThis is an unnecessary rerender and a bottleneck in our application (especially\nif we want to start showing all of the results rather than just the first 500...\nwhich we do want to do eventually). If you enable 6x throttle on the CPU (under\nthe Performance tab in Chrome DevTools) then you'll notice the issue is more\nstark.`]}),`\n`,(0,n.jsxs)(e.p,{children:[\"Your job is to optimize the \",(0,n.jsx)(e.code,{children:\"ListItem\"}),\" component to be memoized via \",(0,n.jsx)(e.code,{children:\"memo\"}),`. Make\nnote of the before/after render times.`]}),`\n`,(0,n.jsx)(e.p,{children:`Make sure to check both the React Profiler and the Chrome DevTools Performance\ntab.`}),`\n`,(0,n.jsx)(e.p,{children:`As with most of these exercises, the code changes are minimal, but the impact\nis significant!`})]})}function l(t={}){let{wrapper:e}=t.components||{};return e?(0,n.jsx)(e,{...t,children:(0,n.jsx)(d,{...t})}):d(t)}function j(t,e){throw new Error(\"Expected \"+(e?\"component\":\"object\")+\" `\"+t+\"` to be defined: you likely forgot to import, pass, or provide it.\")}return g(k);})();\n;return Component;","epicVideoEmbeds",[532],"https://www.epicreact.dev/workshops/react-performance/component-memoization","test",{"_9":535,"_535":536},"script","playwright test --config=./tests/playwright.config.js","dev",{"_9":535,"_539":540,"_236":237},"portNumber",6051,"stackBlitzUrl","https://stackblitz.com/github/epicweb-dev/react-performance/tree/main/exercises/06.rerenders/01.problem.memo?view=editor&title=Component+Memoization+%28problem%29","solutionName",{"_20":147,"_186":471,"_513":545,"_22":148,"_24":149,"_515":546,"_530":547,"_533":549,"_537":550,"_541":552,"_310":341,"_322":311,"_9":336,"_553":-5},"01.solution.memo","var Component=(()=>{var u=Object.create;var i=Object.defineProperty;var f=Object.getOwnPropertyDescriptor;var h=Object.getOwnPropertyNames;var l=Object.getPrototypeOf,x=Object.prototype.hasOwnProperty;var w=(e,t)=>()=>(t||e((t={exports:{}}).exports,t),t.exports),_=(e,t)=>{for(var o in t)i(e,o,{get:t[o],enumerable:!0})},s=(e,t,o,c)=>{if(t&&typeof t==\"object\"||typeof t==\"function\")for(let r of h(t))!x.call(e,r)&&r!==o&&i(e,r,{get:()=>t[r],enumerable:!(c=f(t,r))||c.enumerable});return e};var j=(e,t,o)=>(o=e!=null?u(l(e)):{},s(t||!e||!e.__esModule?i(o,\"default\",{value:e,enumerable:!0}):o,e)),g=e=>s(i({},\"__esModule\",{value:!0}),e);var m=w((b,a)=>{a.exports=_jsx_runtime});var y={};_(y,{default:()=>d,frontmatter:()=>M});var n=j(m()),M=void 0;function p(e){let t={h1:\"h1\",p:\"p\",...e.components},{EpicVideo:o}=t;return o||v(\"EpicVideo\",!0),(0,n.jsxs)(n.Fragment,{children:[(0,n.jsx)(t.h1,{children:\"Component Memoization\"}),`\n`,(0,n.jsx)(o,{url:\"https://www.epicreact.dev/workshops/react-performance/component-memoization/solution\"}),`\n`,(0,n.jsx)(t.p,{children:`\\u{1F468}\\u200D\\u{1F4BC} Great job! You've managed to really improve the performance of our list when\nunrelated updates occur. But what if there are updates to the list itself?\nHmm...`})]})}function d(e={}){let{wrapper:t}=e.components||{};return t?(0,n.jsx)(t,{...e,children:(0,n.jsx)(p,{...e})}):p(e)}function v(e,t){throw new Error(\"Expected \"+(t?\"component\":\"object\")+\" `\"+e+\"` to be defined: you likely forgot to import, pass, or provide it.\")}return g(y);})();\n;return Component;",[548],"https://www.epicreact.dev/workshops/react-performance/component-memoization/solution",{"_9":535,"_535":536},{"_9":535,"_539":551,"_236":237},7051,"https://stackblitz.com/github/epicweb-dev/react-performance/tree/main/exercises/06.rerenders/01.solution.memo?view=editor&title=Component+Memoization+%28solution%29","problemName",{"_322":353,"_320":555,"_336":564},{"_20":151,"_186":473,"_513":556,"_22":152,"_24":153,"_515":557,"_530":558,"_533":560,"_537":561,"_541":563,"_310":341,"_322":353,"_9":320,"_543":155},"02.problem.comparator","var Component=(()=>{var p=Object.create;var s=Object.defineProperty;var b=Object.getOwnPropertyDescriptor;var v=Object.getOwnPropertyNames;var m=Object.getPrototypeOf,y=Object.prototype.hasOwnProperty;var u=(n,e)=>()=>(e||n((e={exports:{}}).exports,e),e.exports),f=(n,e)=>{for(var a in e)s(n,a,{get:e[a],enumerable:!0})},c=(n,e,a,o)=>{if(e&&typeof e==\"object\"||typeof e==\"function\")for(let l of v(e))!y.call(n,l)&&l!==a&&s(n,l,{get:()=>e[l],enumerable:!(o=b(e,l))||o.enumerable});return n};var g=(n,e,a)=>(a=n!=null?p(m(n)):{},c(e||!n||!n.__esModule?s(a,\"default\",{value:n,enumerable:!0}):a,n)),w=n=>c(s({},\"__esModule\",{value:!0}),n);var i=u((N,t)=>{t.exports=_jsx_runtime});var E={};f(E,{default:()=>h,frontmatter:()=>k});var r=g(i()),k=void 0;function d(n){let e={code:\"code\",h1:\"h1\",p:\"p\",pre:\"pre\",span:\"span\",...n.components},{EpicVideo:a}=e;return a||x(\"EpicVideo\",!0),(0,r.jsxs)(r.Fragment,{children:[(0,r.jsx)(e.h1,{children:\"Custom Comparator\"}),`\n`,(0,r.jsx)(a,{url:\"https://www.epicreact.dev/workshops/react-performance/custom-comparator\"}),`\n`,(0,r.jsxs)(e.p,{children:[\"\\u{1F468}\\u200D\\u{1F4BC} We've improved things so the \",(0,r.jsx)(e.code,{children:\"ListItem\"}),` components don't rerender when there\nare unrelated changes, but what if there are changes to the list item state?`]}),`\n`,(0,r.jsx)(e.p,{children:`Hover over one of the list items and notice they all rerender. But we really\nonly need the hovered item to rerender (as well as the one that's no longer\nhighlighted).`}),`\n`,(0,r.jsxs)(e.p,{children:[\"So let's add a custom comparator to the \",(0,r.jsx)(e.code,{children:\"memo\"}),\" call in \",(0,r.jsx)(e.code,{children:\"ListItem\"}),` to only\nrerender when the changed props will affect the output.`]}),`\n`,(0,r.jsx)(e.p,{children:\"Here's an example of the comparator:\"}),`\n`,(0,r.jsx)(e.pre,{\"data-line-numbers\":\"true\",\"data-lang\":\"tsx\",style:{color:\"var(--base05)\",backgroundColor:\"var(--base00)\"},children:(0,r.jsxs)(e.code,{children:[(0,r.jsxs)(e.span,{className:\"codeblock-line\",\"data-line-number\":\"1\",children:[(0,r.jsx)(e.span,{style:{color:\"var(--base0A)\"},children:\"const\"}),\" \",(0,r.jsx)(e.span,{style:{color:\"var(--base08)\"},children:\"Avatar\"}),\" \",(0,r.jsx)(e.span,{style:{color:\"var(--base0E)\"},children:\"=\"}),\" \",(0,r.jsx)(e.span,{style:{color:\"var(--base0D)\"},children:\"memo\"}),\"(\",`\n`]}),(0,r.jsxs)(e.span,{className:\"codeblock-line\",\"data-line-number\":\"2\",children:[\"\t\",(0,r.jsx)(e.span,{style:{color:\"var(--base0D)\"},children:\"function\"}),\" \",(0,r.jsx)(e.span,{style:{color:\"var(--base0D)\"},children:\"Avatar\"}),\"({ \",(0,r.jsx)(e.span,{style:{color:\"var(--base08)\"},children:\"user\"}),\" }\",(0,r.jsx)(e.span,{style:{color:\"var(--base0E)\"},children:\":\"}),\" { \",(0,r.jsx)(e.span,{style:{color:\"var(--base08)\"},children:\"user\"}),(0,r.jsx)(e.span,{style:{color:\"var(--base0E)\"},children:\":\"}),\" \",(0,r.jsx)(e.span,{style:{color:\"var(--base0A)\"},children:\"User\"}),\" }) {\",`\n`]}),(0,r.jsxs)(e.span,{className:\"codeblock-line\",\"data-line-number\":\"3\",children:[\"\t\t\",(0,r.jsx)(e.span,{style:{color:\"var(--base0E)\"},children:\"return\"}),\" <\",(0,r.jsx)(e.span,{style:{color:\"var(--base08)\"},children:\"img\"}),\" \",(0,r.jsx)(e.span,{style:{color:\"var(--base0D)\"},children:\"src\"}),(0,r.jsx)(e.span,{style:{color:\"var(--base0E)\"},children:\"=\"}),(0,r.jsx)(e.span,{style:{color:\"var(--base0F)\"},children:\"{\"}),(0,r.jsx)(e.span,{style:{color:\"var(--base08)\"},children:\"user\"}),\".\",(0,r.jsx)(e.span,{style:{color:\"var(--base08)\"},children:\"avatarUrl\"}),(0,r.jsx)(e.span,{style:{color:\"var(--base0F)\"},children:\"}\"}),\" \",(0,r.jsx)(e.span,{style:{color:\"var(--base0D)\"},children:\"alt\"}),(0,r.jsx)(e.span,{style:{color:\"var(--base0E)\"},children:\"=\"}),(0,r.jsx)(e.span,{style:{color:\"var(--base0F)\"},children:\"{\"}),(0,r.jsx)(e.span,{style:{color:\"var(--base08)\"},children:\"user\"}),\".\",(0,r.jsx)(e.span,{style:{color:\"var(--base08)\"},children:\"name\"}),(0,r.jsx)(e.span,{style:{color:\"var(--base0F)\"},children:\"}\"}),\" />\",`\n`]}),(0,r.jsxs)(e.span,{className:\"codeblock-line\",\"data-line-number\":\"4\",children:[\"\t},\",`\n`]}),(0,r.jsxs)(e.span,{className:\"codeblock-line\",\"data-line-number\":\"5\",children:[\"\t(\",(0,r.jsx)(e.span,{style:{color:\"var(--base08)\"},children:\"prevProps\"}),\", \",(0,r.jsx)(e.span,{style:{color:\"var(--base08)\"},children:\"nextProps\"}),\") \",(0,r.jsx)(e.span,{style:{color:\"var(--base0D)\"},children:\"=>\"}),\" {\",`\n`]}),(0,r.jsxs)(e.span,{className:\"codeblock-line\",\"data-line-number\":\"6\",children:[\"\t\t\",(0,r.jsx)(e.span,{style:{color:\"var(--base0A)\"},children:\"const\"}),\" \",(0,r.jsx)(e.span,{style:{color:\"var(--base08)\"},children:\"avatarUnchanged\"}),\" \",(0,r.jsx)(e.span,{style:{color:\"var(--base0E)\"},children:\"=\"}),`\n`]}),(0,r.jsxs)(e.span,{className:\"codeblock-line\",\"data-line-number\":\"7\",children:[\"\t\t\t\",(0,r.jsx)(e.span,{style:{color:\"var(--base08)\"},children:\"prevProps\"}),\".\",(0,r.jsx)(e.span,{style:{color:\"var(--base0D)\"},children:\"user\"}),\".\",(0,r.jsx)(e.span,{style:{color:\"var(--base08)\"},children:\"avatarUrl\"}),\" \",(0,r.jsx)(e.span,{style:{color:\"var(--base0E)\"},children:\"===\"}),\" \",(0,r.jsx)(e.span,{style:{color:\"var(--base08)\"},children:\"nextProps\"}),\".\",(0,r.jsx)(e.span,{style:{color:\"var(--base0D)\"},children:\"user\"}),\".\",(0,r.jsx)(e.span,{style:{color:\"var(--base08)\"},children:\"avatarUrl\"}),`\n`]}),(0,r.jsxs)(e.span,{className:\"codeblock-line\",\"data-line-number\":\"8\",children:[\"\t\t\",(0,r.jsx)(e.span,{style:{color:\"var(--base0A)\"},children:\"const\"}),\" \",(0,r.jsx)(e.span,{style:{color:\"var(--base08)\"},children:\"nameUnchanged\"}),\" \",(0,r.jsx)(e.span,{style:{color:\"var(--base0E)\"},children:\"=\"}),\" \",(0,r.jsx)(e.span,{style:{color:\"var(--base08)\"},children:\"prevProps\"}),\".\",(0,r.jsx)(e.span,{style:{color:\"var(--base0D)\"},children:\"user\"}),\".\",(0,r.jsx)(e.span,{style:{color:\"var(--base08)\"},children:\"name\"}),\" \",(0,r.jsx)(e.span,{style:{color:\"var(--base0E)\"},children:\"===\"}),\" \",(0,r.jsx)(e.span,{style:{color:\"var(--base08)\"},children:\"nextProps\"}),\".\",(0,r.jsx)(e.span,{style:{color:\"var(--base0D)\"},children:\"user\"}),\".\",(0,r.jsx)(e.span,{style:{color:\"var(--base08)\"},children:\"name\"}),`\n`]}),(0,r.jsxs)(e.span,{className:\"codeblock-line\",\"data-line-number\":\"9\",children:[\"\t\t\",(0,r.jsx)(e.span,{style:{color:\"var(--base03)\"},children:\"// return true if we don't want to re-render\"}),`\n`]}),(0,r.jsxs)(e.span,{className:\"codeblock-line\",\"data-line-number\":\"10\",children:[\"\t\t\",(0,r.jsx)(e.span,{style:{color:\"var(--base0E)\"},children:\"return\"}),\" \",(0,r.jsx)(e.span,{style:{color:\"var(--base08)\"},children:\"avatarUnchanged\"}),\" \",(0,r.jsx)(e.span,{style:{color:\"var(--base0E)\"},children:\"&&\"}),\" \",(0,r.jsx)(e.span,{style:{color:\"var(--base08)\"},children:\"nameUnchanged\"}),`\n`]}),(0,r.jsxs)(e.span,{className:\"codeblock-line\",\"data-line-number\":\"11\",children:[\"\t},\",`\n`]}),(0,r.jsxs)(e.span,{className:\"codeblock-line\",\"data-line-number\":\"12\",children:[\")\",`\n`]})]})}),`\n`,(0,r.jsxs)(e.p,{children:[\"So even if the user object changes, the \",(0,r.jsx)(e.code,{children:\"Avatar\"}),` component will only rerender if\nthe `,(0,r.jsx)(e.code,{children:\"avatarUrl\"}),\" or \",(0,r.jsx)(e.code,{children:\"name\"}),\" properties change.\"]}),`\n`,(0,r.jsx)(e.p,{children:`By default, React just checks the reference of the props, so by providing a\ncustom comparator, we override that default behavior to have a more fine-grained\ncontrol over when the component should rerender.`}),`\n`,(0,r.jsxs)(e.p,{children:[\"So let's add a custom comparator to the \",(0,r.jsx)(e.code,{children:\"ListItem\"}),` component so it only rerenders\nwhen absolutely necessary.`]}),`\n`,(0,r.jsx)(e.p,{children:`Pull up the React Profiler and the DevTools Performance tab to see the impact\nof this optimization as you hover over different list items.`})]})}function h(n={}){let{wrapper:e}=n.components||{};return e?(0,r.jsx)(e,{...n,children:(0,r.jsx)(d,{...n})}):d(n)}function x(n,e){throw new Error(\"Expected \"+(e?\"component\":\"object\")+\" `\"+n+\"` to be defined: you likely forgot to import, pass, or provide it.\")}return w(E);})();\n;return Component;",[559],"https://www.epicreact.dev/workshops/react-performance/custom-comparator",{"_9":535,"_535":536},{"_9":535,"_539":562,"_236":237},6052,"https://stackblitz.com/github/epicweb-dev/react-performance/tree/main/exercises/06.rerenders/02.problem.comparator?view=editor&title=Custom+Comparator+%28problem%29",{"_20":155,"_186":473,"_513":565,"_22":156,"_24":157,"_515":566,"_530":567,"_533":569,"_537":570,"_541":572,"_310":341,"_322":353,"_9":336,"_553":-5},"02.solution.comparator","var Component=(()=>{var u=Object.create;var i=Object.defineProperty;var f=Object.getOwnPropertyDescriptor;var l=Object.getOwnPropertyNames;var h=Object.getPrototypeOf,x=Object.prototype.hasOwnProperty;var w=(t,e)=>()=>(e||t((e={exports:{}}).exports,e),e.exports),_=(t,e)=>{for(var o in e)i(t,o,{get:e[o],enumerable:!0})},s=(t,e,o,c)=>{if(e&&typeof e==\"object\"||typeof e==\"function\")for(let r of l(e))!x.call(t,r)&&r!==o&&i(t,r,{get:()=>e[r],enumerable:!(c=f(e,r))||c.enumerable});return t};var j=(t,e,o)=>(o=t!=null?u(h(t)):{},s(e||!t||!t.__esModule?i(o,\"default\",{value:t,enumerable:!0}):o,t)),y=t=>s(i({},\"__esModule\",{value:!0}),t);var p=w((M,a)=>{a.exports=_jsx_runtime});var C={};_(C,{default:()=>d,frontmatter:()=>b});var n=j(p()),b=void 0;function m(t){let e={h1:\"h1\",p:\"p\",...t.components},{EpicVideo:o}=e;return o||g(\"EpicVideo\",!0),(0,n.jsxs)(n.Fragment,{children:[(0,n.jsx)(e.h1,{children:\"Custom Comparator\"}),`\n`,(0,n.jsx)(o,{url:\"https://www.epicreact.dev/workshops/react-performance/custom-comparator/solution\"}),`\n`,(0,n.jsx)(e.p,{children:`\\u{1F468}\\u200D\\u{1F4BC} Great! The performance is better! Unfortunately, that custom comparator is\nkinda complex. I wonder if we could simplify it a bit...`})]})}function d(t={}){let{wrapper:e}=t.components||{};return e?(0,n.jsx)(e,{...t,children:(0,n.jsx)(m,{...t})}):m(t)}function g(t,e){throw new Error(\"Expected \"+(e?\"component\":\"object\")+\" `\"+t+\"` to be defined: you likely forgot to import, pass, or provide it.\")}return y(C);})();\n;return Component;",[568],"https://www.epicreact.dev/workshops/react-performance/custom-comparator/solution",{"_9":535,"_535":536},{"_9":535,"_539":571,"_236":237},7052,"https://stackblitz.com/github/epicweb-dev/react-performance/tree/main/exercises/06.rerenders/02.solution.comparator?view=editor&title=Custom+Comparator+%28solution%29",{"_322":356,"_320":574,"_336":583},{"_20":159,"_186":480,"_513":575,"_22":160,"_24":161,"_515":576,"_530":577,"_533":579,"_537":580,"_541":582,"_310":341,"_322":356,"_9":320,"_543":163},"03.problem.primitives","var Component=(()=>{var p=Object.create;var s=Object.defineProperty;var b=Object.getOwnPropertyDescriptor;var v=Object.getOwnPropertyNames;var m=Object.getPrototypeOf,y=Object.prototype.hasOwnProperty;var u=(n,e)=>()=>(e||n((e={exports:{}}).exports,e),e.exports),f=(n,e)=>{for(var r in e)s(n,r,{get:e[r],enumerable:!0})},o=(n,e,r,c)=>{if(e&&typeof e==\"object\"||typeof e==\"function\")for(let l of v(e))!y.call(n,l)&&l!==r&&s(n,l,{get:()=>e[l],enumerable:!(c=b(e,l))||c.enumerable});return n};var k=(n,e,r)=>(r=n!=null?p(m(n)):{},o(e||!n||!n.__esModule?s(r,\"default\",{value:n,enumerable:!0}):r,n)),w=n=>o(s({},\"__esModule\",{value:!0}),n);var i=u((D,t)=>{t.exports=_jsx_runtime});var N={};f(N,{default:()=>h,frontmatter:()=>g});var a=k(i()),g=void 0;function d(n){let e={code:\"code\",h1:\"h1\",p:\"p\",pre:\"pre\",span:\"span\",...n.components},{EpicVideo:r}=e;return r||E(\"EpicVideo\",!0),(0,a.jsxs)(a.Fragment,{children:[(0,a.jsx)(e.h1,{children:\"Primitives\"}),`\n`,(0,a.jsx)(r,{url:\"https://www.epicreact.dev/workshops/react-performance/primitives\"}),`\n`,(0,a.jsx)(e.p,{children:`\\u{1F468}\\u200D\\u{1F4BC} I would love to have the performance improvement without all the complexity\nof the custom comparator function.`}),`\n`,(0,a.jsxs)(e.p,{children:[\"The default comparator function is a simple \",(0,a.jsx)(e.code,{children:\"===\"}),` comparison. So if we changed\nthe props a bit, we could take advantage of this.`]}),`\n`,(0,a.jsx)(e.p,{children:\"Remember our Avatar example before?\"}),`\n`,(0,a.jsx)(e.pre,{\"data-line-numbers\":\"true\",\"data-lang\":\"tsx\",style:{color:\"var(--base05)\",backgroundColor:\"var(--base00)\"},children:(0,a.jsxs)(e.code,{children:[(0,a.jsxs)(e.span,{className:\"codeblock-line\",\"data-line-number\":\"1\",children:[(0,a.jsx)(e.span,{style:{color:\"var(--base0A)\"},children:\"const\"}),\" \",(0,a.jsx)(e.span,{style:{color:\"var(--base08)\"},children:\"Avatar\"}),\" \",(0,a.jsx)(e.span,{style:{color:\"var(--base0E)\"},children:\"=\"}),\" \",(0,a.jsx)(e.span,{style:{color:\"var(--base0D)\"},children:\"memo\"}),\"(\",`\n`]}),(0,a.jsxs)(e.span,{className:\"codeblock-line\",\"data-line-number\":\"2\",children:[\"\t\",(0,a.jsx)(e.span,{style:{color:\"var(--base0D)\"},children:\"function\"}),\" \",(0,a.jsx)(e.span,{style:{color:\"var(--base0D)\"},children:\"Avatar\"}),\"({ \",(0,a.jsx)(e.span,{style:{color:\"var(--base08)\"},children:\"user\"}),\" }\",(0,a.jsx)(e.span,{style:{color:\"var(--base0E)\"},children:\":\"}),\" { \",(0,a.jsx)(e.span,{style:{color:\"var(--base08)\"},children:\"user\"}),(0,a.jsx)(e.span,{style:{color:\"var(--base0E)\"},children:\":\"}),\" \",(0,a.jsx)(e.span,{style:{color:\"var(--base0A)\"},children:\"User\"}),\" }) {\",`\n`]}),(0,a.jsxs)(e.span,{className:\"codeblock-line\",\"data-line-number\":\"3\",children:[\"\t\t\",(0,a.jsx)(e.span,{style:{color:\"var(--base0E)\"},children:\"return\"}),\" <\",(0,a.jsx)(e.span,{style:{color:\"var(--base08)\"},children:\"img\"}),\" 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/>\",`\n`]}),(0,a.jsxs)(e.span,{className:\"codeblock-line\",\"data-line-number\":\"4\",children:[\"\t},\",`\n`]}),(0,a.jsxs)(e.span,{className:\"codeblock-line\",\"data-line-number\":\"5\",children:[\"\t(\",(0,a.jsx)(e.span,{style:{color:\"var(--base08)\"},children:\"prevProps\"}),\", \",(0,a.jsx)(e.span,{style:{color:\"var(--base08)\"},children:\"nextProps\"}),\") \",(0,a.jsx)(e.span,{style:{color:\"var(--base0D)\"},children:\"=>\"}),\" {\",`\n`]}),(0,a.jsxs)(e.span,{className:\"codeblock-line\",\"data-line-number\":\"6\",children:[\"\t\t\",(0,a.jsx)(e.span,{style:{color:\"var(--base0A)\"},children:\"const\"}),\" \",(0,a.jsx)(e.span,{style:{color:\"var(--base08)\"},children:\"avatarUnchanged\"}),\" 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\",(0,a.jsx)(e.span,{style:{color:\"var(--base0E)\"},children:\"=\"}),\" \",(0,a.jsx)(e.span,{style:{color:\"var(--base08)\"},children:\"prevProps\"}),\".\",(0,a.jsx)(e.span,{style:{color:\"var(--base0D)\"},children:\"user\"}),\".\",(0,a.jsx)(e.span,{style:{color:\"var(--base08)\"},children:\"name\"}),\" \",(0,a.jsx)(e.span,{style:{color:\"var(--base0E)\"},children:\"===\"}),\" \",(0,a.jsx)(e.span,{style:{color:\"var(--base08)\"},children:\"nextProps\"}),\".\",(0,a.jsx)(e.span,{style:{color:\"var(--base0D)\"},children:\"user\"}),\".\",(0,a.jsx)(e.span,{style:{color:\"var(--base08)\"},children:\"name\"}),`\n`]}),(0,a.jsxs)(e.span,{className:\"codeblock-line\",\"data-line-number\":\"9\",children:[\"\t\t\",(0,a.jsx)(e.span,{style:{color:\"var(--base03)\"},children:\"// return true if we don't want to re-render\"}),`\n`]}),(0,a.jsxs)(e.span,{className:\"codeblock-line\",\"data-line-number\":\"10\",children:[\"\t\t\",(0,a.jsx)(e.span,{style:{color:\"var(--base0E)\"},children:\"return\"}),\" \",(0,a.jsx)(e.span,{style:{color:\"var(--base08)\"},children:\"avatarUnchanged\"}),\" \",(0,a.jsx)(e.span,{style:{color:\"var(--base0E)\"},children:\"||\"}),\" \",(0,a.jsx)(e.span,{style:{color:\"var(--base08)\"},children:\"nameUnchanged\"}),`\n`]}),(0,a.jsxs)(e.span,{className:\"codeblock-line\",\"data-line-number\":\"11\",children:[\"\t},\",`\n`]}),(0,a.jsxs)(e.span,{className:\"codeblock-line\",\"data-line-number\":\"12\",children:[\")\",`\n`]})]})}),`\n`,(0,a.jsx)(e.p,{children:\"We could change the props for this component to be primitives instead of objects.\"}),`\n`,(0,a.jsx)(e.pre,{\"data-line-numbers\":\"true\",\"data-lang\":\"tsx\",style:{color:\"var(--base05)\",backgroundColor:\"var(--base00)\"},children:(0,a.jsxs)(e.code,{children:[(0,a.jsxs)(e.span,{className:\"codeblock-line\",\"data-line-number\":\"1\",children:[(0,a.jsx)(e.span,{style:{color:\"var(--base0A)\"},children:\"const\"}),\" \",(0,a.jsx)(e.span,{style:{color:\"var(--base08)\"},children:\"Avatar\"}),\" 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But you'll want to make sure the\ntests continue to pass when you're finished.`})})]})}function h(n={}){let{wrapper:e}=n.components||{};return e?(0,a.jsx)(e,{...n,children:(0,a.jsx)(d,{...n})}):d(n)}function E(n,e){throw new Error(\"Expected \"+(e?\"component\":\"object\")+\" `\"+n+\"` to be defined: you likely forgot to import, pass, or provide it.\")}return w(N);})();\n;return Component;",[578],"https://www.epicreact.dev/workshops/react-performance/primitives",{"_9":535,"_535":536},{"_9":535,"_539":581,"_236":237},6053,"https://stackblitz.com/github/epicweb-dev/react-performance/tree/main/exercises/06.rerenders/03.problem.primitives?view=editor&title=Primitives+%28problem%29",{"_20":163,"_186":475,"_513":584,"_22":164,"_24":165,"_515":585,"_530":586,"_533":588,"_537":589,"_541":591,"_310":341,"_322":356,"_9":336,"_553":-5},"03.solution.primitives","var Component=(()=>{var u=Object.create;var i=Object.defineProperty;var h=Object.getOwnPropertyDescriptor;var f=Object.getOwnPropertyNames;var l=Object.getPrototypeOf,x=Object.prototype.hasOwnProperty;var w=(t,e)=>()=>(e||t((e={exports:{}}).exports,e),e.exports),_=(t,e)=>{for(var o in e)i(t,o,{get:e[o],enumerable:!0})},s=(t,e,o,c)=>{if(e&&typeof e==\"object\"||typeof e==\"function\")for(let r of f(e))!x.call(t,r)&&r!==o&&i(t,r,{get:()=>e[r],enumerable:!(c=h(e,r))||c.enumerable});return t};var j=(t,e,o)=>(o=t!=null?u(l(t)):{},s(e||!t||!t.__esModule?i(o,\"default\",{value:t,enumerable:!0}):o,t)),b=t=>s(i({},\"__esModule\",{value:!0}),t);var m=w((M,a)=>{a.exports=_jsx_runtime});var y={};_(y,{default:()=>d,frontmatter:()=>g});var n=j(m()),g=void 0;function p(t){let e={code:\"code\",h1:\"h1\",p:\"p\",...t.components},{EpicVideo:o}=e;return o||v(\"EpicVideo\",!0),(0,n.jsxs)(n.Fragment,{children:[(0,n.jsx)(e.h1,{children:\"Primitive Values\"}),`\n`,(0,n.jsx)(o,{url:\"https://www.epicreact.dev/workshops/react-performance/primitives/solution\"}),`\n`,(0,n.jsxs)(e.p,{children:[\"\\u{1F468}\\u200D\\u{1F4BC} Great job! 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06. Optimize Rendering/Elaboration