Earlier I had a Class component, so I didn't face any issues while using lifecycle methods, but after converting to useEffect hooks, I am facing the initial render issue which I don't want to happen.
Class
componentDidMount() {
this.setState({
patchVal:this.props.patchTaskVal,
startTime:this.props.patchStartTime,
setEndTime:this.props.patchEndTime
})
}
componentDidUpdate(prevProps) {
if (prevProps.patchTaskVal !== this.props.patchTaskVal) {
this.callValidation()
}
if (prevProps.closeTask !== this.props.closeTask) {
this.setState({
showValue:false,
progressValue:[],
startTime:new Date(),
setEndTime:""
})
}
if (prevProps.patchStartTime !== this.props.patchStartTime || prevProps.endTime !== this.props.endTime && this.props.endTime !== "") {
this.setState({
startTime:this.props.patchStartTime,
setEndTime:parseInt(this.props.endTime)
})
}
}
Functional
const [patchTaskVal, setPatchTaskVal]=useState(/*initial value */)
const [startTime, setStartTime]=useState()
const [endTime, setEndTime] = useState()
**// I want only this useEffect to run on the initial render**
useEffect(() => {
setPatchTaskVal(props.patchTaskVal)
...//set other states
}, [])
useEffect(() => {
callValidation()
}, [props.patchTaskVal])
useEffect(() => {
//setShowValue...
}, [props.closeTask])
useEffect(() => {
if (props.endTime != "") {
// set states...
}
}, [props.patchStartTime,props.endTime])
Here I am facing an issue where all the useEffects are running on the initial render, Please suggest a solution for this so that only the first useEffect will run on the initial render and all other useEffects will run according to its dependency prop values.
CodePudding user response:
You basically need a ref
which will tell you whether this is the first render on not. Refs values persist over rerenders. You can start with a truthy
value and toggle it to false
after the first render (using a useEffect
with an empty array[]). Based on that you can run your desired code.
You can also put the whole thing in a custom hook:
import { useEffect, useRef } from "react";
const useOnUpdate = (callback, deps) => {
const isFirst = useRef(true);
useEffect(() => {
if (!isFirst.current) {
callback();
}
}, deps);
useEffect(() => {
isFirst.current = false;
}, []);
};
export default useOnUpdate;
You can call this hook in your component like :
useOnUpdate(() => {
console.log(prop);
}, [prop]);
In the hook:
After the initial render, both useEffect
s run. But when the first effect runs the value of the isFirst.current
is true. So the callback is not called. The second useEffect
also runs and sets isFirst.current
to false.
Now in subsequent renders only the first useEffect
run (when dependencies change), and isFirst.current
is false now so callback
is executed.
The order of the two useEffects
is very important here. Otherwise, in the useEffect
with deps
, isFirst.current
will be true even after the first render.
CodePudding user response:
try this...
let init = true;
useEffect( ()=>{
if(init) {
setPatchTaskVal(props.patchTaskVal)
init = false;
...//set other states}
}, [])
useEffect( ()=> {
!init && callValidation()
},[props.patchTaskVal])
useEffect( ()=>{
//!init && setShowValue...
},[props.closeTask])
useEffect( ()=>{
if(props.endTime!="" && !init){
// set states...
}
},[props.patchStartTime,props.endTime])
CodePudding user response:
Hope my understanding is right about your question.
Why not just add a if statement
to check the state
is not undefined
or default value
useEffect( ()=> {
if (props.patchTaskVal) {
callValidation()
}
},[props.patchTaskVal])
useEffect( ()=>{
if (props.closeTask) {
//setShowValue...
}
},[props.closeTask])
useEffect( ()=>{
if(props.patchStartTime){
// set states...
}
if(props.endTime){
// set states...
}
},[props.patchStartTime,props.endTime]
And according your class component,
this.setState({
patchVal:this.props.patchTaskVal,
startTime:this.props.patchStartTime,
setEndTime:this.props.patchEndTime
})
The function component should map props to component's state. Like this
const [patchTaskVal, setPatchTaskVal]=useState(props.patchTaskVal)
const [startTime, setStartTime]=useState(props.patchStartTime)
const [endTime, setEndTime] = useState(props.patchEndTime)