why-did-you-render monkey patches React to notify you about avoidable re-renders. (Works with React Native as well.)
For example, when you pass style={{width: '100%'}} to a big pure component and make it always re-render:
It can also help you to simply track when and why a certain component re-renders.
- You can read more about the library >> HERE <<.
- Part 2 - Common fixing scenarios this library can help to eliminate can be found >> HERE <<.
- Part 3 - React Hooks - Understand and fix hooks issues >> HERE <<.
- Part 4 - React-Redux - Understand and fix react-redux issues >> HERE <<.
You can test the library in the official sandbox >> HERE <<.
The required React version for the library is 16.12 but it is expected to work with older versions as well.
For versions before 16.8 turn off hooks support by using
trackHooks: falseinwhyDidYouRender's init options.*
npm install @welldone-software/why-did-you-render --save
or
yarn add @welldone-software/why-did-you-render
Execute whyDidYouRender with React as its first argument before any React element is created.
import React from 'react';
if (process.env.NODE_ENV !== 'production') {
const whyDidYouRender = require('@welldone-software/why-did-you-render');
whyDidYouRender(React);
}Mark any component you want to be notified about their "redundant" re-renders with whyDidYouRender like this:
class BigListPureComponent extends React.PureComponent {
static whyDidYouRender = true
render(){
return (
//some heavy render you want to ensure doesn't happen if its not neceserry
)
}
}Or like this:
const BigListPureComponent = props => (
<div>
//some heavy component you want to ensure doesn't happen if its not neceserry
</div>
)
BigListPureComponent.whyDidYouRender = trueYou can also pass an object to specify more advanced settings:
EnhancedMenu.whyDidYouRender = {
logOnDifferentValues: true,
customName: 'Menu'
}-
logOnDifferentValues:Normally, only re-renders that are caused by equal values in props / state trigger notifications:
render(<Menu a={1}/>) render(<Menu a={1}/>)
This option will trigger notifications even if they occurred because of different props / state (Thus, because of "legit" re-renders):
render(<Menu a={1}/>) render(<Menu a={2}/>)
-
customName:Sometimes the name of the component can be very inconvenient. For example:
const EnhancedMenu = withPropsOnChange(withPropsOnChange(withStateHandlers(withPropsOnChange(withState(withPropsOnChange(lifecycle(withPropsOnChange(withPropsOnChange(onlyUpdateForKeys(LoadNamespace(Connect(withState(withState(withPropsOnChange(lifecycle(withPropsOnChange(withHandlers(withHandlers(withHandlers(withHandlers(Connect(lifecycle(Menu)))))))))))))))))))))))
will have the display name:
withPropsOnChange(withPropsOnChange(withStateHandlers(withPropsOnChange(withState(withPropsOnChange(lifecycle(withPropsOnChange(withPropsOnChange(onlyUpdateForKeys(LoadNamespace(Connect(withState(withState(withPropsOnChange(lifecycle(withPropsOnChange(withHandlers(withHandlers(withHandlers(withHandlers(Connect(lifecycle(Menu)))))))))))))))))))))))
To prevent polluting the console, and any other reason, you can change it using
customName.
Optionally you can pass in options as the second parameter. The following options are available:
include: [RegExp, ...](nullby default)exclude: [RegExp, ...](nullby default)trackHooks: truetrackExtraHooks: []logOnDifferentValues: falsehotReloadBufferMs: 500onlyLogs: falsecollapseGroups: falsetitleColordiffNameColordiffPathColortrackAllComponents: falsenotifier: ({Component, displayName, prevProps, prevState, nextProps, nextState, reason, options}) => void
You can include or exclude tracking for re-renders for components
by their displayName with the include and exclude options.
Notice: exclude takes priority over both include and whyDidYouRender statics on components.
For example, the following code is used to track all redundant re-renders that are caused by React-Redux:
whyDidYouRender(React, { include: [/^ConnectFunction/] });You can turn off tracking of hooks changes.
Understand and fix hook issues >> HERE <<.
Adding extra hooks to track for "redundant" results:
whyDidYouRender(React, {trackExtraHooks: [
[Redux, 'useSelector']
]});Normally, you only want notifications about component re-renders when their props and state are the same, because it means these re-renders could have been avoided. But you can also track all re-renders, even on different state/props.
render(<BigListPureComponent a={1}/>)
render(<BigListPureComponent a={2}/>)
// this will only cause whyDidYouRender notifications for {logOnDifferentValues: true}Time in milliseconds to ignore updates after a hot reload is detected.
We can't currently know exactly if a render was triggered by hot reload,
so instead, we ignore all updates for hotReloadBufferMs (default: 500) after a hot reload.
If you don't want to use console.group to group logs by component, you can print them as simple logs.
Grouped logs can start collapsed:
Controls the colors used in the console notifications
You can create a custom notifier if the default one does not suite your needs.
If you are building for latest browsers (or using es6 classes without building) you don't transpile the "class" keyword.
This causes an error because the library uses transpiled classes, and transpiled classes currently can't extend native classes.
To fix this, use the "no-classes-transpile" dist:
import React from 'react';
if (process.env.NODE_ENV !== 'production') {
const whyDidYouRender = require('@welldone-software/why-did-you-render/dist/no-classes-transpile/umd/whyDidYouRender.min.js');
whyDidYouRender(React);
}Since connect hoists statics, if you add WDYR to the inner component, it is also added to the HOC component where complex hooks are running.
To fix this, add the whyDidYouRender = true static to a component after the connect:
const SimpleComponent = ({a}) => <div data-testid="foo">{a.b}</div>)
// not before the connect:
// SimpleComponent.whyDidYouRender = true
const ConnectedSimpleComponent = connect(
state => ({a: state.a})
)(SimpleComponent)
// after the connect:
SimpleComponent.whyDidYouRender = trueInspired by the following previous work:
https://github.com/maicki/why-did-you-update which i had the chance to maintain for some time.
https://github.com/garbles/why-did-you-update where A deep dive into React perf debugging is credited for the idea.
This library is MIT licensed.