<Profiler>

<Profilerid="App"onRender={onRender}>
<App/>
</Profiler>

• Reference
  • <Profiler>
  • onRender callback
• Usage
  • Measuring rendering performance programmatically
  • Measuring different parts of the application

Reference

<Profiler>

Wrap a component tree in a<Profiler> to measure its rendering performance.

<Profilerid="App"onRender={onRender}>
<App/>
</Profiler>

Props

• id: A string identifying the part of the UI you are measuring.
• onRender: AnonRender callback that React calls every time components within the profiled tree update. It receives information about what was rendered and how much time it took.

Caveats

• Profiling adds some additional overhead, soit is disabled in the production build by default. To opt into production profiling, you need to enable aspecial production build with profiling enabled.

onRender callback

React will call youronRender callback with information about what was rendered.

functiononRender(id,phase,actualDuration,baseDuration,startTime,commitTime){
// Aggregate or log render timings...
}

Parameters

• id: The stringid prop of the<Profiler> tree that has just committed. This lets you identify which part of the tree was committed if you are using multiple profilers.
• phase:"mount","update" or"nested-update". This lets you know whether the tree has just been mounted for the first time or re-rendered due to a change in props, state, or Hooks.
• actualDuration: The number of milliseconds spent rendering the<Profiler> and its descendants for the current update. This indicates how well the subtree makes use of memoization (e.g.memo anduseMemo). 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: The number of milliseconds estimating how much time it would take to re-render the entire<Profiler> subtree without any optimizations. It is calculated by summing up the most recent render durations of each component in the tree. This value estimates a worst-case cost of rendering (e.g. the initial mount or a tree with no memoization). CompareactualDuration against it to see if memoization is working.
• startTime: A numeric timestamp for when React began rendering the current update.
• commitTime: A numeric timestamp for when React committed the current update. This value is shared between all profilers in a commit, enabling them to be grouped if desirable.

Usage

Measuring rendering performance programmatically

Wrap the<Profiler> component around a React tree to measure its rendering performance.

<App>
<Profilerid="Sidebar"onRender={onRender}>
<Sidebar/>
</Profiler>
<PageContent/>
</App>

It requires two props: anid (string) and anonRender callback (function) which React calls any time a component within the tree “commits” an update.

Measuring different parts of the application

You can use multiple<Profiler> components to measure different parts of your application:

<App>
<Profilerid="Sidebar"onRender={onRender}>
<Sidebar/>
</Profiler>
<Profilerid="Content"onRender={onRender}>
<Content/>
</Profiler>
</App>

You can also nest<Profiler> components:

<App>
<Profilerid="Sidebar"onRender={onRender}>
<Sidebar/>
</Profiler>
<Profilerid="Content"onRender={onRender}>
<Content>
<Profilerid="Editor"onRender={onRender}>
<Editor/>
</Profiler>
<Preview/>
</Content>
</Profiler>
</App>

Although<Profiler> is a lightweight component, it should be used only when necessary. Each use adds some CPU and memory overhead to an application.