Spread Operator not copying results in React - reactjs

Question

I am trying to update setState in a for loop, but for some reason state isn't being copied it's just being replaced. There should be 2 clients, instead I am getting one. Can anyone tell me why this is happening? The console.log is returning both clients.
const handleViewClients = () => {
for (let i = 0; i < clients.length; i++) {
console.log(clients[i].clientid);
fetch("http://localhost:3005/all-clients/" + clients[i].clientid)
.then((response) => response.json())
.then((result) => {
console.log(result);
setBarbersClient({
...barbersClient,
client: result,
});
});
}
};
I have also tried this... The console.log is returning what I need
Promise.all(
clients.map((client) =>
fetch("http://localhost:3005/all-clients/" + client.clientid)
)
)
.then((resp) => resp.json())
.then((result) => {
console.log(result.username)
setBarbersClient({
...barbersClient,
client: result,
});
});
Here is the route from the server side
app.get("/all-clients/:clientid", (req, res) => {
db.NewClientsx.findOne({
where: {
id: req.params.clientid,
},
}).then((response) => {
res.json(response);
});
});

Answer 1

There some fundamental concepts of sync vs. async code that you aren't accounting for here. State changing (and fetching) is asynchronous, so it won't run until after this synchronous loop has finished being executed (during which the state value will remain unchanged). Also, it's a bad idea to change state in a loop, for this reason and others.
Fetch all the clients, then do one state change at the end with all the fetched data. You can utilise things like Promise.all and Promise.spread to achieve this. Here's an example of doing multiple fetches then dealing with the results in one batch: How can I fetch an array of URLs with Promise.all?

Answer 2

You're making two distinct mistakes of which either is enough to cause the behaviour you're seeing.
1. You're overwriting the client property.
Every time you call the setter function you're overwriting the previous value of the client property. You'll need some data structure that supports multiple values like a map:
setBarbersClient({
...barbersClient,
clients: {
...barbersClient.clients,
[result.id]: result
},
});
You will need to change your render logic somewhat to accomodate the new data structure.
2. You're using a stale reference.
When you access barbersClient its setter may have already been called with a different value and your reference to it still refers to the value of the previous run of the render function. You can make sure your reference is fresh by using a set state action callback.
setBarbersClient(previousValue => {
...previousValue,
clients: {
...previousValue.clients,
[result.id]: result
},
});
previousValue will never be stale inside the set state action function body.