how to set state array using react hooks

how to set state array using react hooks

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(state => [...state, newMessage])

To insert new element at the begining of the list

const addMessage = (newMessage) => setMessages(state => [newMessage, ...state])

how to set state array using react hooks, How to use useState multiple ways — useState with arrays, useState with There are a bunch of React hooks, but useState is the workhorse of the bunch. you create a single piece of state associated with that component. A typical code example using React Hooks to keep a list of items would initialize React state using a call like useState ([]). “ useState is a Hook […] We call it inside a function component to add

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])

4 Examples of the useState Hook, Learn how to manipulate arrays in React state by using JavaScript array If you are interested in seeing this with function components and React Hooks, setState() method on a React component to update React's state. They let you use state and other React features without writing a class. The introduction page used this example to get familiar with Hooks: import React , { useState } from 'react' ; function Example ( ) { // Declare a new state variable, which we'll call "count" const [ count , setCount ] = useState ( 0 ) ; return ( < div > < p > You clicked { count } times </ p > < button onClick = { ( ) => setCount ( count + 1 ) } > Click me </ button > </ div > ) ; }

There is no real need to use the prevState, you could just do:

setMessages([...messages, newMessage])

How to manage React State with Arrays, when i try to set an array state, I'm working on Ionic react, should be work the same? Read Duration: 5:55 Posted: May 20, 2019 That's only one way of providing a fallback for an array being null. As alternative, you can also use React's conditional rendering for it.. The second question, which asks how to push an empty array in React state, involves manipulating the state with this.setState().

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

let newState = [...messages, 'Hi buddy'];

If state is an object and you need to update a property in it

let newState = Object.assign({}, message, {name: 'Michael Scott'});

React Hooks Tutorial - 5 - useState with array, They let you use state and other React features without writing a class. The introduction page used this example to get familiar with Hooks: In a function component, we have no this , so we can't assign or read this.state . Instead When we declare a state variable with useState , it returns a pair — an array with two items. React Hooks are a broad set of tools in the React front-end JavaScript library that run custom functions when a component's props change. Since this method of state management doesn't require you to use classes, developers can use Hooks to write shorter, more readable code that is easy to share and maintain.

setMessages(prevState => [...prevState, newMessage])

Using the State Hook – React, That includes effects capturing state that belongs to that render. So what happens in your initial example is that: First render has messages set to� UseEffect is the primary solution. But as Darryl mentioned, using useEffect and passing in state as the second parameter has one flaw, the component will run on the initialization process. If you just want the callback function to run using the updated state's value, you could set a local constant and use that in both the setState and the callback.

React Hooks useState updating an array � Issue #15041 � facebook , This functionality is possible due to React's new Hooks. setState() call in class components, except that it doesn't merge the old and new� let nextInLine = [array with an object]; setPastChat(pastChat.concat(nextInLine)); } This code works just fine, but when I try to run this setPastChat() in a loop (while or for loop) it just replaces the last item instead of concat() it. I'm using concat because push() does not work as well. So I have something like this:

Fetching Data and Updating State with Hooks, See how the useState Hook allows for state variables in functional There are two types of components in React: class and functional It returns an array, where the first element is the state variable and You'd have to do something like this (assuming the properties of the object are state and setState ): When you have deep objects, you end up deep cloning them for immutability, which can be quite expensive in React. Why? Once you deep clone the state, React will recalculate and re-render everything that depends on the variables, even though they haven't changed! So, before trying to solve your issue, think how you can flatten the state first.

A guide to useState in React, Delphi queries related to “react hooks update object in array in state”. react useState set one element of array � usestate to store an array � hook� By calling React.useState inside a function component, you create a single piece of state associated with that component. (every hook starts with the word “use”; a call to useState literally lets you “use state” in a function component) In classes, the state is always an object, and you can store multiple values in that object.