Fetch data before component render, Reactjs - reactjs

Question

I am having a slight issue with my react code. I want the data to be completely fetched before rendering. However, I have tried various ways such as 'setGroupLoaded to true' after the async call, but it is still not working. When the component first mounts, 'groupLoaded == false and myGroup == [],', then it goes to the next conditional statement where 'groupLoaded == true' but the myGroup [] is still empty. I was expecting the myGroup [] to be filled with data since groupLoaded is true. Please I need help with it.
function CreateGroup({ currentUser }) {
const [name, setName] = useState("");
const [myGroup, setMyGroup] = useState([]);
const [groupAdded, setGroupAdded] = useState(false);
const [groupLoaded, setGroupLoaded] = useState(false);
const handleChange = (e) => {
const { value, name } = e.target;
setName({
[name]: value,
});
};
useEffect(() => {
const fetchGroupCreated = async () => {
let groupArr = await fetchMyGroup(currentUser);
setMyGroup(groupArr);
};
fetchGroupCreated();
setGroupLoaded(true);
return () => {
setMyGroup([]);
};
}, [currentUser.id, groupAdded, deleteGroupStatus]);
useEffect(() => {
let groupId = myGroup.length ? myGroup[0].id : "";
let groupName = myGroup.length ? myGroup[0].groupName : "";
if (myGroup.length) {
JoinGroup(currentUser, groupId, groupName);
setTimeout(() => fetchGroupMembers(), 3000);
}
}, [myGroup]);
let itemsToRender;
if (groupLoaded && myGroup.length) {
itemsToRender = myGroup.map((item) => {
return <Group key={item.id} item={item} deleteGroup={deleteGroup} />;
});
} else if (groupLoaded && myGroup.length === 0) {
itemsToRender = (
<div>
<form onSubmit={handleSubmit}>
<div className="form-group">
<label htmlFor="exampleInputTitle">Group Name</label>
<input
type="text"
className="form-control"
name="name"
id="name"
aria-describedby="TitleHelp"
onChange={handleChange}
/>
</div>
<button type="submit" className="btn btn-primary">
Add group{" "}
</button>
</form>
</div>
);
}
return (
<div>
<h3>{currentUser ? currentUser.displayName : ""}</h3>
{itemsToRender}
</div>
);
}

Answer 1

The problem is here:
useEffect(() => {
const fetchGroupCreated = async () => {
let groupArr = await fetchMyGroup(currentUser);
setMyGroup(groupArr);
};
fetchGroupCreated();
setGroupLoaded(true);
return () => {
setMyGroup([]);
};
}, [currentUser.id, groupAdded, deleteGroupStatus]);
When you call setGroupLoaded(true), the first call to setMyGroup(groupArr) hasn't happened yet because fetchMyGroup(currentUser) is asynchronous. If you've never done this before, I highly recommend putting in some logging statements, to see the order in which is executes:
useEffect(() => {
const fetchGroupCreated = async () => {
console.log("Got data")
let groupArr = await fetchMyGroup(currentUser);
setMyGroup(groupArr);
};
console.log("Before starting to load")
fetchGroupCreated();
setGroupLoaded(true);
console.log("After starting to load")
return () => {
setMyGroup([]);
};
}, [currentUser.id, groupAdded, deleteGroupStatus]);
The output will be:
Before starting to load
After starting to load
Got data
This is probably not the order you expected, but explains exactly why you get groupLoaded == true, but the myGroup is still empty.
The solution (as Nick commented) is to move the setGroupLoaded(true) into the callback, so that it runs after the data is retrieved:
const fetchGroupCreated = async () => {
let groupArr = await fetchMyGroup(currentUser);
setMyGroup(groupArr);
setGroupLoaded(true);
};
fetchGroupCreated();
An alternative approach may be to await the call to fetchGroupCreated(). I'm not sure if it'll work, but if it does it'll be simpler:
await fetchGroupCreated();