How to Use componentDidMount() in Functional Component to execute a function - reactjs

Question

I have a functional component which had a button to call a method in it. Now i want to get rid of the button and call that method without any actions once the component loads.
I am making API calls inside this method and passing on the results to another component.
Also I am replacing the button with a progress bar meaning when a "search" is taking place, display the progress bar but I am having no luck. What am I doing wrong ?
export const Search = (props) => {
const { contacts, setContacts, onSearchComplete } = props;
const [msgBox, setMsgBox] = useState(null);
const [loading, setLoading] = useState(false);
const onSearch = async () => {
setLoading(true);
const emails = contacts
.filter(x => x.isChecked)
.map(item => item.emailAddress);
try {
const searchResults = await AppApi.searchMany(emails);
let userList = [];
for (let i = 0; i < searchResults.length; i++) {
//process the list and filter
}
userList = [...userList, ..._users];
}
onSearchComplete(userList); //passing the results.
} catch (err) {
console.log({ err });
setMsgBox({ message: `${err.message}`, type: 'error' });
}
setLoading(false);
}
return (
<Box>
{loading ? <LinearProgress /> : <Box>{msgBox && (<a style={{ cursor: 'pointer' }} onClick={() => setMsgBox(null)} title="Click to dismiss"><MessageBox type={msgBox.type || 'info'}>{msgBox.message}</MessageBox></a>)}</Box>}
/*{onSearch()}*/ // function that was executed onclick.
</Box>
);
}

Answer 1

You will want to use the useEffect hook with an empty dependency array which will make it act as componentDidMount source.
export const Search = (props) => {
const { contacts, setContacts, onSearchComplete } = props;
const [msgBox, setMsgBox] = useState(null);
const [loading, setLoading] = useState(false);
const onSearch = async () => {
...
}
useEffect(() => {
onSearch();
}, []);
return (
<Box>
{loading ? <LinearProgress /> : <Box>{msgBox && (<a style={{ cursor: 'pointer' }} onClick={() => setMsgBox(null)} title="Click to dismiss"><MessageBox type={msgBox.type || 'info'}>{msgBox.message}</MessageBox></a>)}</Box>}
</Box>
);
}