Can I update a component's props in React.js?
JavascriptReactjsPropertiesJavascript Problem Overview
After starting to work with React.js, it seems like props
are intended to be static (passed in from the parent component), while state
changes based upon events. However, I noticed in the docs a reference to componentWillReceiveProps
, which specifically includes this example:
componentWillReceiveProps: function(nextProps) {
this.setState({
likesIncreasing: nextProps.likeCount > this.props.likeCount
});
}
This seems to imply that the properties CAN change on a component based upon the comparison of nextProps
to this.props
. What am I missing? How do props change, or am I mistaken about where this gets called?
Javascript Solutions
Solution 1 - Javascript
A component cannot update its own props unless they are arrays or objects (having a component update its own props even if possible is an anti-pattern), but can update its state and the props of its children.
For instance, a Dashboard has a speed
field in its state, and passes it to a Gauge child thats displays this speed. Its render
method is just return <Gauge speed={this.state.speed} />
. When the Dashboard calls this.setState({speed: this.state.speed + 1})
, the Gauge is re-rendered with the new value for speed
.
Just before this happens, Gauge's componentWillReceiveProps
is called, so that the Gauge has a chance to compare the new value to the old one.
Solution 2 - Javascript
PROPS
> A React component should use props to store information that can be > changed, but can only be changed by a different component.
STATE
> A React component should use state to store information that the > component itself can change.
A good example is already provided by Valéry.
Solution 3 - Javascript
Props can change when a component's parent renders the component again with different properties. I think this is mostly an optimization so that no new component needs to be instantiated.
Solution 4 - Javascript
Much has changed with hooks, e.g. componentWillReceiveProps
turned into useEffect
+useRef
(as shown in this other SO answer), but Props are still Read-Only, so only the caller method should update it.
Solution 5 - Javascript
Trick to update props if they are array :
import React, { Component } from 'react';
import {
AppRegistry,
StyleSheet,
Text,
View,
Button
} from 'react-native';
class Counter extends Component {
constructor(props) {
super(props);
this.state = {
count: this.props.count
}
}
increment(){
console.log("this.props.count");
console.log(this.props.count);
let count = this.state.count
count.push("new element");
this.setState({ count: count})
}
render() {
return (
<View style={styles.container}>
<Text>{ this.state.count.length }</Text>
<Button
onPress={this.increment.bind(this)}
title={ "Increase" }
/>
</View>
);
}
}
Counter.defaultProps = {
count: []
}
export default Counter
const styles = StyleSheet.create({
container: {
flex: 1,
justifyContent: 'center',
alignItems: 'center',
backgroundColor: '#F5FCFF',
},
welcome: {
fontSize: 20,
textAlign: 'center',
margin: 10,
},
instructions: {
textAlign: 'center',
color: '#333333',
marginBottom: 5,
},
});
Solution 6 - Javascript
If you use recompose
, use mapProps
to make new props derived from incoming props
Example:
import { compose, mapProps } from 'recompose';
const SomeComponent = ({ url, onComplete }) => (
{url ? (
<View />
) : null}
)
export default compose(
mapProps(({ url, storeUrl, history, ...props }) => ({
...props,
onClose: () => {
history.goBack();
},
url: url || storeUrl,
})),
)(SomeComponent);