react hooks setTimeout after setState - reactjs

Question

I recently wanted to design an input component with react hooks.
The component would check validation after entering input in 0.5 second.
my code like
const inputField = ({ name, type, hint, inputValue, setInput }) => {
// if there is default value, set default value to state
const [value, setValue] = useState(inputValue);
// all of validation are true for testing
const validCheck = () => true;
let timeout;
const handleChange = e => {
clearTimeout(timeout);
const v = e.target.value;
setValue(v);
timeout = setTimeout(() => {
// if valid
if (validCheck()) {
// do something...
}
}, 500);
};
return (
<SCinputField>
<input type={type} onChange={handleChange} />
</SCinputField>
);
};
unfortunately, it's not worked, because the timeout variable would renew every time after setValue.
I found react-hooks provide some feature like useRef to store variable.
Should I use it or shouldn't use react-hooks in this case?
Update
add useEffect
const inputField = ({ name, type, hint, inputValue, setInput }) => {
// if there is default value, set default value to state
const [value, setValue] = useState(inputValue);
// all of validation are true for testing
const validCheck = () => true;
let timeout;
const handleChange = e => {
const v = e.target.value;
setValue(v);
};
// handle timeout
useEffect(() => {
let timeout;
if (inputValue !== value) {
timeout = setTimeout(() => {
const valid = validCheck(value);
console.log('fire after a moment');
setInput({
key: name,
valid,
value
});
}, 1000);
}
return () => {
clearTimeout(timeout);
};
});
return (
<SCinputField>
<input type={type} onChange={handleChange} />
</SCinputField>
);
};
It looks worked, but I am not sure about it's a right way to use.

Answer 1

Here's how I would do it:
import React, {useState, useEffect, useRef} from 'react';
function InputField() {
const [value, setValue] = useState(''); // STATE FOR THE INPUT VALUE
const timeoutRef = useRef(null); // REF TO KEEP TRACK OF THE TIMEOUT
function validate() { // VALIDATE FUNCTION
console.log('Validating after 500ms...');
}
useEffect(() => { // EFFECT TO RUN AFTER CHANGE IN VALUE
if (timeoutRef.current !== null) { // IF THERE'S A RUNNING TIMEOUT
clearTimeout(timeoutRef.current); // THEN, CANCEL IT
}
timeoutRef.current = setTimeout(()=> { // SET A TIMEOUT
timeoutRef.current = null; // RESET REF TO NULL WHEN IT RUNS
value !== '' ? validate() : null; // VALIDATE ANY NON-EMPTY VALUE
},500); // AFTER 500ms
},[value]); // RUN EFFECT AFTER CHANGE IN VALUE
return( // SIMPLE TEXT INPUT
<input type='text'
value={value}
onChange={(e) => setValue(e.target.value)}
/>
);
}
WORKING EXAMPLE ON SNIPPET BELOW:
function InputField() {
const [value, setValue] = React.useState('');
const timeoutRef = React.useRef(null);
function validate() {
console.log('Validating after 500ms...');
}
React.useEffect(() => {
if (timeoutRef.current !== null) {
clearTimeout(timeoutRef.current);
}
timeoutRef.current = setTimeout(()=> {
timeoutRef.current = null;
value !== '' ? validate() : null;
},500);
},[value]);
return(
<input type='text' value={value} onChange={(e) => setValue(e.target.value)}/>
);
}
ReactDOM.render(<InputField/>, document.getElementById('root'));
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/16.8.3/umd/react.production.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react-dom/16.8.3/umd/react-dom.production.min.js"></script>
<div id="root"/>

Answer 2

You don't need to keep the reference to the timeout between renders. You can just return a function from the useEffect to clear it:
React.useEffect(() => {
const timeout = setTimeout(()=> {
if (value !== '') {
validate();
}
}, 500);
return () => {
clearTimeout(timeout); // this guarantees to run right before the next effect
}
},[value, validate]);
Also, don't forget to pass all the dependencies to the effect, including the validate function.
Ideally, you would pass the value as a parameter to the validate function: validate(value) - this way, the function has fewer dependencies, and could even be pure and moved outside the component.
Alternatively, if you have internal dependencies (like another setState or an onError callback from props), create the validate function with a useCallback() hook :
const validate = useCallback((value) => {
// do something with the `value` state
if ( /* value is NOT valid */ ) {
onError(); // call the props for an error
} else {
onValid();
}
}, [onError, onValid]); // and any other dependencies your function may use
This will keep the same function reference between the renders if the dependencies don't change.

Answer 3

You can move timeout variable inside handleChange method.
const inputField = ({ name, type, hint, inputValue, setInput }) => {
// if there is default value, set default value to state
const [value, setValue] = useState(inputValue);
// all of validation are true for testing
const validCheck = () => true;
const handleChange = e => {
let timeout;
clearTimeout(timeout);
const v = e.target.value;
setValue(v);
timeout = setTimeout(() => {
// if valid
if (validCheck()) {
// do something...
}
}, 500);
};
return (
<SCinputField>
<input type={type} onChange={handleChange} />
</SCinputField>
);
};