Thanks in advance. I have a state array as below.
I need to add an item to state array, I came across that we need not do state mutation. How do i set state with prevState.
const [messages, setMessages] = React.useState(
[
{
_id: 12,
createdAt: new Date(),
text: 'All good',
user: {
_id: 1,
name: 'Sian Pol',
}
},
{
_id: 21,
createdAt: "2019-11-10 22:21",
text: 'Hello user',
user: {
_id: 2,
name: 'User New'
}
}]
)
How to to i call the set State to append this state array.
Something like this?
setMessages(previousState => ({...stat
Can anyone help me in getting the above line code.
To insert new element at the end of the list
const addMessage = (newMessage) => setMessages(oldMessages => [...oldMessages, newMessage])
To insert new element at the begining of the list
const addMessage = (newMessage) => setMessages(oldMessages => [newMessage, ...oldMessages])
More readable and cleaner solution it would be:
Create a variable that holds a copy of the actual state:
If state is an array and you need to add an element in it
const newState = [...messages, 'Hi buddy'];
setMessages(newState);
or
setMessages(prevState => [...prevState, "Hi Buddy"]);
If state is an object and you need to update a property in it
const newState = Object.assign({}, message, {name: 'Michael Scott'});
setMessages(newState);
or
setMessages(prevState => {...prevState, name: "Michael Scott" });
Your state is an array so you will need to spread your previous state into a new array and add the new message using [...prevState, newMessage]
What you try to do is return an object, because {}
is a code block so you need to wrap it inside ()
if you return an object which is what you are trying to do
setMessages(prevState => [...prevState, newMessage])
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