componentdidmount in functional component react code example
Example 1: how to use componentdidmount in functional component
// passing an empty array as second argument triggers the callback in useEffect
// only after the initial render thus replicating `componentDidMount` lifecycle behaviour
useEffect(() => {
if(!props.fetched) {
props.fetchRules();
}
console.log('mount it!');
}, []);
// componentDidUpdate
useEffect({
your code here
})
// For componentDidUpdate
useEffect(() => {
// Your code here
}, [yourDependency]);
// For componentWillUnmount
useEffect(() => {
// componentWillUnmount
return () => {
// Your code here
}
}, [yourDependency]);
Example 2: react useEffect
import React, { useEffect } from 'react';
export const App: React.FC = () => {
useEffect(() => {
}, [/*Here can enter some value to call again the content inside useEffect*/])
return (
<div>Use Effect!</div>
);
}
Example 3: how to use useeffect
import React, { useState, useEffect } from 'react';
function Example() {
const [count, setCount] = useState(0);
// Similar to componentDidMount and componentDidUpdate:
useEffect(() => {
// Update the document title using the browser API
document.title = `You clicked ${count} times`;
});
return (
<div>
<p>You clicked {count} times</p>
<button onClick={() => setCount(count + 1)}>
Click me
</button>
</div>
);
}
Example 4: componentwillunmount hooks
useEffect(() => {
window.addEventListener('mousemove', () => {});
// returned function will be called on component unmount
return () => {
window.removeEventListener('mousemove', () => {})
}
}, [])
Example 5: useeffect componentdidmount
useEffect(() => {
messagesRef.on('child added', snapshot => {
const message = snapshot.val();
message.key = snapshot.key;
setMessages(messages.concat(message)); // See Note 1
}, []); // See Note 2