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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,119 @@ | ||
| --- | ||
| id: profiler | ||
| title: Profiler API | ||
| layout: docs | ||
| category: Reference | ||
| permalink: docs/profiler.html | ||
| --- | ||
|
|
||
| The `Profiler` measures how often a React application renders and what the "cost" of rendering is. | ||
| Its purpose is to help identify parts of an application that are slow and may benefit from [optimizations such as memoization](https://reactjs.org/docs/hooks-faq.html#how-to-memoize-calculations). | ||
|
|
||
| > Note: | ||
| > | ||
| > Profiling adds some additional overhead, so **it is disabled in [the production build](https://reactjs.org/docs/optimizing-performance.html#use-the-production-build)**. | ||
| > | ||
| > To opt into production profiling, React provides a special production build with profiling enabled. | ||
| > Read more about how to use this build at [fb.me/react-profiling](https://fb.me/react-profiling) | ||
| ## Usage | ||
|
|
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| A `Profiler` can be added anywhere in a React tree to measure the cost of rendering that part of the tree. | ||
| It requires two props: an `id` (string) and an `onRender` callback (function) which React calls any time a component within the tree "commits" an update. | ||
|
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| For example, to profile a `Navigation` component and its descendants: | ||
|
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| ```js{3} | ||
| render( | ||
| <App> | ||
| <Profiler id="Navigation" onRender={callback}> | ||
| <Navigation {...props} /> | ||
| </Profiler> | ||
| <Main {...props} /> | ||
| </App> | ||
| ); | ||
| ``` | ||
|
|
||
| Multiple `Profiler` components can be used to measure different parts of an application: | ||
| ```js{3,6} | ||
| render( | ||
| <App> | ||
| <Profiler id="Navigation" onRender={callback}> | ||
| <Navigation {...props} /> | ||
| </Profiler> | ||
| <Profiler id="Main" onRender={callback}> | ||
| <Main {...props} /> | ||
| </Profiler> | ||
| </App> | ||
| ); | ||
| ``` | ||
|
|
||
| `Profiler` components can also be nested to measure different components within the same subtree: | ||
| ```js{2,6,8} | ||
| render( | ||
| <App> | ||
| <Profiler id="Panel" onRender={callback}> | ||
| <Panel {...props}> | ||
| <Profiler id="Content" onRender={callback}> | ||
| <Content {...props} /> | ||
| </Profiler> | ||
| <Profiler id="PreviewPane" onRender={callback}> | ||
| <PreviewPane {...props} /> | ||
| </Profiler> | ||
| </Panel> | ||
| </Profiler> | ||
| </App> | ||
| ); | ||
| ``` | ||
|
|
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| > Note | ||
| > | ||
| > Although `Profiler` is a light-weight component, it should be used only when necessary; each use adds some CPU and memory overhead to an application. | ||
| ## `onRender` Callback | ||
|
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||
| The `Profiler` requires an `onRender` function as a prop. | ||
| React calls this function any time a component within the profiled tree "commits" an update. | ||
| It receives parameters describing what was rendered and how long it took. | ||
|
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||
| ```js | ||
| function onRenderCallback( | ||
| id, // the "id" prop of the Profiler tree that has just committed | ||
| phase, // either "mount" (if the tree just mounted) or "update" (if it re-rendered) | ||
| actualDuration, // time spent rendering the committed update | ||
| baseDuration, // estimated time to render the entire subtree without memoization | ||
| startTime, // when React began rendering this update | ||
| commitTime, // when React committed this update | ||
| interactions // the Set of interactions belonging to this update | ||
| ) { | ||
| // Aggregate or log render timings... | ||
| } | ||
| ``` | ||
|
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| Let's take a closer look at each of the props: | ||
|
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| * **`id: string`** - | ||
| The `id` prop of the `Profiler` tree that has just committed. | ||
| This can be used to identify which part of the tree was committed if you are using multiple profilers. | ||
| * **`phase: "mount" | "update"`** - | ||
| Identifies whether the tree has just been mounted for the first time or re-rendered due to a change in props, state, or hooks. | ||
| * **`actualDuration: number`** - | ||
| Time spent rendering the `Profiler` and its descendants for the current update. | ||
| This indicates how well the subtree makes use of memoization (e.g. [`React.memo`](/docs/react-api.html#reactmemo), [`useMemo`](/docs/hooks-reference.html#usememo), [`shouldComponentUpdate`](/docs/hooks-faq.html#how-do-i-implement-shouldcomponentupdate)). | ||
| Ideally this value should decrease significantly after the initial mount as many of the descendants will only need to re-render if their specific props change. | ||
| * **`baseDuration: number`** - | ||
| Duration of the most recent `render` time for each individual component within the `Profiler` tree. | ||
| This value estimates a worst-case cost of rendering (e.g. the initial mount or a tree with no memoization). | ||
| * **`startTime: number`** - | ||
| Timestamp when React began rendering the current update. | ||
| * **`commitTime: number`** - | ||
| Timestamp when React committed the current update. | ||
| This value is shared between all profilers in a commit, enabling them to be grouped if desirable. | ||
| * **`interactions: Set`** - | ||
| Set of ["interactions"](http://fb.me/react-interaction-tracing) that were being traced the update was scheduled (e.g. when `render` or `setState` were called). | ||
|
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| > Note | ||
| > | ||
| > Interactions can be used to identify the cause of an update, although the API for tracing them is still experimental. | ||
| > | ||
| > Learn more about it at [fb.me/react-interaction-tracing](http://fb.me/react-interaction-tracing) |
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