Related
I know this question was asked before. But if I follow the accepted answer it doesn't work for me. Here is my code:-
export class SurveyForm extends Component {
constructor(props) {
super(props);
this.state = {
isSelected: false,
selectedVal: 0,
selectedRatingIndex: -1,
};
this.handleSubmit = this.handleSubmit.bind(this);
}
onClick={() => {
// this is the recommended way of setting state. This doesn't work.
this.setState((prevState) => ({
selectedRatingIndex: (prevState.selectedRatingIndex = val),
}));
this.setState((prevState) => ({
isSelected: (prevState.isSelected = !this.state.isSelected),
}));
// other code removed.
}
But if I do as follows:-
this.setState({
selectedRatingIndex: (this.state.selectedRatingIndex = val),
});
this.setState({
isSelected: (this.state.isSelected = !this.state.isSelected),
});
It works and it shows the warning Do not mutate state directly. Use setState() I am confused, what should one do in this case?
When you call setState with an object, that object should just contain the new values.
this.setState({
selectedRatingIndex: val,
});
this.setState({
isSelected: !this.state.isSelected, // it would be better to use a prevState callback instead of this.state
});
When you use a prevState callback, you return an object of new values derived from prevState.
this.setState((prevState) => ({
selectedRatingIndex: val, // there is no point to a prevState callback here because prevState is unused
}));
this.setState(prevState => ({
isSelected: !prevState.isSelected,
}));
When you do something like this:
this.setState({
selectedRatingIndex: (this.state.selectedRatingIndex = val),
});
You are mutating the state by setting this.state.selectedRatingIndex = val with = which is the assignment operator. The returned value from that assignment is the new value (val) so that's why it kinda-sorta works: you are essentially calling this.setState({ selectedRatingIndex: val }), but you're mutating the state in the process which you should not do.
I am new to react and created a login form with a few set of validations to raise errors in case of blank username or password. On the very first instance, when nothing is inserted and the Submit is clicked, it works fine. But once the value is changed with a value inserted by the user and then deleting from the text input, the variable gets a value of "" and never gets back to null value. This avoids my special treatment where I inserted !this.state.username. It gets stuck at that moment and the form submission goes anyway to the server. I have tried trim as well but it didn't work
class LoginClassComponent extends React.Component {
constructor(props) {
super(props);
this.state = {
username: this.props.username,
password: this.props.password,
errorUsername: null,
errorPassword: null,
};
this.handleValidation = this.handleValidation.bind(this);
this.handleChange = this.handleChange.bind(this);
}
//assign textbox values to props
handleChange = (e) => {
this.setState({
[e.target.name]: [e.target.value],
});
};
//handle input validation
handleValidation = (event) => {
if (!this.state.username) {
this.setState({ errorUsername: "Please enter User Name" });
event.preventDefault();
}
if (!this.state.password) {
this.setState({ errorPassword: "Please enter Password" });
event.preventDefault();
}
Your handleChange is incorrect, you should remove the brackets around value:
handleChange = (e) => {
this.setState({
[e.target.name]: e.target.value
});
};
for this scenario I would go with function components and hooks, but for the sake of simplicity and not knowing what the rest of your implementation looks like, I'd go as follows.
Assuming you are triggering handleValidation either on field blur or on submit click, try modifying it like so:
handleValidation = (event) => {
event.preventDefault();
let errorUsername = null;
let errorPassword = null;
if (event.target.name === 'username') {
errorUsername = (event.target.value === '') ? "Please enter User Name" : null;
} else if (event.target.name === 'password') {
errorPassword = (event.target.value === '') ? "Please enter Password" : null;
}
this.setState({ errorUsername, errorPassword });
}
Let me know if you need any further assistance.
Cheers! 🍻
Is it at all possible to update object's properties with setState?
Something like:
this.state = {
jasper: { name: 'jasper', age: 28 },
}
I have tried:
this.setState({jasper.name: 'someOtherName'});
and this:
this.setState({jasper: {name: 'someothername'}})
The first results in a syntax error and the second just does nothing. Any ideas?
There are multiple ways of doing this, since state update is a async operation, so to update the state object, we need to use updater function with setState.
1- Simplest one:
First create a copy of jasper then do the changes in that:
this.setState(prevState => {
let jasper = Object.assign({}, prevState.jasper); // creating copy of state variable jasper
jasper.name = 'someothername'; // update the name property, assign a new value
return { jasper }; // return new object jasper object
})
Instead of using Object.assign we can also write it like this:
let jasper = { ...prevState.jasper };
2- Using spread syntax:
this.setState(prevState => ({
jasper: { // object that we want to update
...prevState.jasper, // keep all other key-value pairs
name: 'something' // update the value of specific key
}
}))
Note: Object.assign and Spread Operator creates only shallow copy, so if you have defined nested object or array of objects, you need a different approach.
Updating nested state object:
Assume you have defined state as:
this.state = {
food: {
sandwich: {
capsicum: true,
crackers: true,
mayonnaise: true
},
pizza: {
jalapeno: true,
extraCheese: false
}
}
}
To update extraCheese of pizza object:
this.setState(prevState => ({
food: {
...prevState.food, // copy all other key-value pairs of food object
pizza: { // specific object of food object
...prevState.food.pizza, // copy all pizza key-value pairs
extraCheese: true // update value of specific key
}
}
}))
Updating array of objects:
Lets assume you have a todo app, and you are managing the data in this form:
this.state = {
todoItems: [
{
name: 'Learn React Basics',
status: 'pending'
}, {
name: 'Check Codebase',
status: 'pending'
}
]
}
To update the status of any todo object, run a map on the array and check for some unique value of each object, in case of condition=true, return the new object with updated value, else same object.
let key = 2;
this.setState(prevState => ({
todoItems: prevState.todoItems.map(
el => el.key === key? { ...el, status: 'done' }: el
)
}))
Suggestion: If object doesn't have a unique value, then use array index.
This is the fastest and the most readable way:
this.setState({...this.state.jasper, name: 'someothername'});
Even if this.state.jasper already contains a name property, the new name name: 'someothername' with be used.
Use spread operator and some ES6 here
this.setState({
jasper: {
...this.state.jasper,
name: 'something'
}
})
I know there are a lot of answers here, but I'm surprised none of them create a copy of the new object outside of setState, and then simply setState({newObject}). Clean, concise and reliable. So in this case:
const jasper = { ...this.state.jasper, name: 'someothername' }
this.setState(() => ({ jasper }))
Or for a dynamic property (very useful for forms)
const jasper = { ...this.state.jasper, [VarRepresentingPropertyName]: 'new value' }
this.setState(() => ({ jasper }))
Using hook we can do following way
const [student, setStudent] = React.useState({name: 'jasper', age: 28});
setStudent((prevState) => ({
...prevState,
name: 'newName',
}));
I used this solution.
If you have a nested state like this:
this.state = {
formInputs:{
friendName:{
value:'',
isValid:false,
errorMsg:''
},
friendEmail:{
value:'',
isValid:false,
errorMsg:''
}
}
}
you can declare the handleChange function that copy current status and re-assigns it with changed values
handleChange(el) {
let inputName = el.target.name;
let inputValue = el.target.value;
let statusCopy = Object.assign({}, this.state);
statusCopy.formInputs[inputName].value = inputValue;
this.setState(statusCopy);
}
here the html with the event listener. Make sure to use the same name used into state object (in this case 'friendName')
<input type="text" onChange={this.handleChange} " name="friendName" />
try this,it should work fine
this.setState(Object.assign(this.state.jasper,{name:'someOtherName'}));
Create a state object
this.state = {
objName: {
propertyOne: "",
propertyTwo: ""
}
};
Update state using setState
this.setState(prevState => ({
objName: {
...prevState.objName,
propertyOne: "Updated Value",
propertyTwo: "Updated value"
}
}));
this is another solution using immer immutabe utility, very suited for deeply nested objects with ease, and you should not care about mutation
this.setState(
produce(draft => {
draft.jasper.name = 'someothername'
})
)
Using hooks in Functional Component:
const [state, setState] = useState({jasper: { name: 'jasper', age: 28 }})
const nameChangeHandler = () => {
setState(prevState => ({
...prevState,
prevState.jasper.name = "Anurag",
prevState.jasper.age = 28
})
)
}
In these cases It is recommended to use callback-based approach to update the state , because using this approach it is ensured that previously states are fully updated and we're updating based on previously updated state.
The first case is indeed a syntax error.
Since I can't see the rest of your component, it's hard to see why you're nesting objects in your state here. It's not a good idea to nest objects in component state. Try setting your initial state to be:
this.state = {
name: 'jasper',
age: 28
}
That way, if you want to update the name, you can just call:
this.setState({
name: 'Sean'
});
Will that achieve what you're aiming for?
For larger, more complex data stores, I would use something like Redux. But that's much more advanced.
The general rule with component state is to use it only to manage UI state of the component (e.g. active, timers, etc.)
Check out these references:
https://facebook.github.io/react/docs/react-component.html#state
https://facebook.github.io/react/docs/state-and-lifecycle.html
In case of updating an object where keys are string
e.g. let say your state object is
serviceDays: {
Sunday: true,
Monday: true,
Tuesday: false,
Wednesday: true,
Thurday: false,
Friday: true,
Saturday: true
}
so you can update in following way
const onDayClick = day => {
const { serviceDays } = this.state
this.setState(prevState => ({
serviceDays: {
...prevState.serviceDays,
[day]: serviceDays[day] ? false : true
}
}))
}
Another option: define your variable out of the Jasper object and then just call a variable.
Spread operator: ES6
this.state = { jasper: { name: 'jasper', age: 28 } }
let foo = "something that needs to be saved into state"
this.setState(prevState => ({
jasper: {
...jasper.entity,
foo
}
})
You can try with this:
this.setState(prevState => {
prevState = JSON.parse(JSON.stringify(this.state.jasper));
prevState.name = 'someOtherName';
return {jasper: prevState}
})
or for other property:
this.setState(prevState => {
prevState = JSON.parse(JSON.stringify(this.state.jasper));
prevState.age = 'someOtherAge';
return {jasper: prevState}
})
Or you can use handleChage function:
handleChage(event) {
const {name, value} = event.target;
this.setState(prevState => {
prevState = JSON.parse(JSON.stringify(this.state.jasper));
prevState[name] = value;
return {jasper: prevState}
})
}
and HTML code:
<input
type={"text"}
name={"name"}
value={this.state.jasper.name}
onChange={this.handleChange}
/>
<br/>
<input
type={"text"}
name={"age"}
value={this.state.jasper.age}
onChange={this.handleChange}
/>
You can try with this:
(Note: name of input tag === field of object)
<input name="myField" type="text"
value={this.state.myObject.myField}
onChange={this.handleChangeInpForm}>
</input>
-----------------------------------------------------------
handleChangeInpForm = (e) => {
let newObject = this.state.myObject;
newObject[e.target.name] = e.target.value;
this.setState({
myObject: newObject
})
}
Simple and dynamic way.
This will do the job, but you need to set all the ids to the parent so the parent will point to the name of the object, being id = "jasper" and name the name of the input element = property inside of the object jasper.
handleChangeObj = ({target: { id , name , value}}) => this.setState({ [id]: { ...this.state[id] , [name]: value } });
Without using Async and Await Use this...
funCall(){
this.setState({...this.state.jasper, name: 'someothername'});
}
If you using with Async And Await use this...
async funCall(){
await this.setState({...this.state.jasper, name: 'someothername'});
}
Also, following Alberto Piras solution, if you don't want to copy all the "state" object:
handleChange(el) {
let inputName = el.target.name;
let inputValue = el.target.value;
let jasperCopy = Object.assign({}, this.state.jasper);
jasperCopy[inputName].name = inputValue;
this.setState({jasper: jasperCopy});
}
Try with this:
const { jasper } = this.state; //Gets the object from state
jasper.name = 'A new name'; //do whatever you want with the object
this.setState({jasper}); //Replace the object in state
By using the input html input name attribute we can have a more dynamic approach in order to update an object properties.
DOM
html input name attribute
<input type="text" name="fname" handleChange={(e: any) => { updatePerson(e) }}/>
<input type="text" name="lname" handleChange={(e: any) => { updatePerson(e) }}/>
React / TSX
object.assign
const [person, setPerson] = useState<IPerson>({});
function updatePerson(e: React.ChangeEvent<HTMLInputElement>): void {
const { name, value } = e.currentTarget;
setPerson(prevState => {
const newState = Object.assign(person, { [name]: value })
return { ...prevState, ...newState };
});
}
Sample FC:
const [formData, setformData] = useState({
project_admin_permissions: {
task_forms: false,
auto_assign_rules: false,
project_notes: true,
alerts: false,
update_criteria: true,
project_flow: false,
reports: false,
}
})
const handleChangeCheckBox = (e) => {
setformData({
...formData, project_admin_permissions: { ...formData.project_admin_permissions, [e.target.name]: e.target.checked }
})
}
This setup worked for me:
let newState = this.state.jasper;
newState.name = 'someOtherName';
this.setState({newState: newState});
console.log(this.state.jasper.name); //someOtherName
Your second approach doesn't work because {name: 'someothername'} equals {name: 'someothername', age: undefined}, so theundefined would overwrite original age value.
When it comes to change state in nested objects, a good approach would be Immutable.js
this.state = {
jasper: Record({name: 'jasper', age: 28})
}
const {jasper} = this.state
this.setState({jasper: jasper.set(name, 'someothername')})
I have the following component that is submitting new posts. The form is using materiail-ui. I can successfully change the state. But when I submit the form, it gave me the error such that {state is empty} error. But on render event, I tried to console log the state, and I can see the state is changing whenever I type in the new values. Below is the sample of code. For the full codes you can check in my github , which is https://github.com/HtunHtunHtet/reactProject2/blob/master/client/src/components/add_post.js. Thanks in advance.
class AddPost extends Component {
state = {
postCategory: "react",
postTitle: "",
postAuthor: "",
postContent: ""
};
handleChange = (event, index, postCategory) => this.setState({postCategory});
handleSubmit(e){
e.preventDefault();
console.log(this.state);
const data = {
timestamp: Date.now(),
title: this.state.postTitle,
body: this.state.postContent,
author: this.state.postAuthor,
category: this.state.postCategory,
deleted: false,
voteScore: 1
};
this.props.fetchAddPost(data);
this.props.history.push("/");
}
handleInputChange = e => {
const target = e.target;
const value = target.value;
const name = target.name;
this.setState({
[name]: value
});
};
Make handleSubmit a arrow function Or bind it to the component’s “this” in the constructor. Doing either of this will make sure that “this” refers to your Component, when you use “this” in handleSubmit.
Is it at all possible to update object's properties with setState?
Something like:
this.state = {
jasper: { name: 'jasper', age: 28 },
}
I have tried:
this.setState({jasper.name: 'someOtherName'});
and this:
this.setState({jasper: {name: 'someothername'}})
The first results in a syntax error and the second just does nothing. Any ideas?
There are multiple ways of doing this, since state update is a async operation, so to update the state object, we need to use updater function with setState.
1- Simplest one:
First create a copy of jasper then do the changes in that:
this.setState(prevState => {
let jasper = Object.assign({}, prevState.jasper); // creating copy of state variable jasper
jasper.name = 'someothername'; // update the name property, assign a new value
return { jasper }; // return new object jasper object
})
Instead of using Object.assign we can also write it like this:
let jasper = { ...prevState.jasper };
2- Using spread syntax:
this.setState(prevState => ({
jasper: { // object that we want to update
...prevState.jasper, // keep all other key-value pairs
name: 'something' // update the value of specific key
}
}))
Note: Object.assign and Spread Operator creates only shallow copy, so if you have defined nested object or array of objects, you need a different approach.
Updating nested state object:
Assume you have defined state as:
this.state = {
food: {
sandwich: {
capsicum: true,
crackers: true,
mayonnaise: true
},
pizza: {
jalapeno: true,
extraCheese: false
}
}
}
To update extraCheese of pizza object:
this.setState(prevState => ({
food: {
...prevState.food, // copy all other key-value pairs of food object
pizza: { // specific object of food object
...prevState.food.pizza, // copy all pizza key-value pairs
extraCheese: true // update value of specific key
}
}
}))
Updating array of objects:
Lets assume you have a todo app, and you are managing the data in this form:
this.state = {
todoItems: [
{
name: 'Learn React Basics',
status: 'pending'
}, {
name: 'Check Codebase',
status: 'pending'
}
]
}
To update the status of any todo object, run a map on the array and check for some unique value of each object, in case of condition=true, return the new object with updated value, else same object.
let key = 2;
this.setState(prevState => ({
todoItems: prevState.todoItems.map(
el => el.key === key? { ...el, status: 'done' }: el
)
}))
Suggestion: If object doesn't have a unique value, then use array index.
This is the fastest and the most readable way:
this.setState({...this.state.jasper, name: 'someothername'});
Even if this.state.jasper already contains a name property, the new name name: 'someothername' with be used.
Use spread operator and some ES6 here
this.setState({
jasper: {
...this.state.jasper,
name: 'something'
}
})
I know there are a lot of answers here, but I'm surprised none of them create a copy of the new object outside of setState, and then simply setState({newObject}). Clean, concise and reliable. So in this case:
const jasper = { ...this.state.jasper, name: 'someothername' }
this.setState(() => ({ jasper }))
Or for a dynamic property (very useful for forms)
const jasper = { ...this.state.jasper, [VarRepresentingPropertyName]: 'new value' }
this.setState(() => ({ jasper }))
Using hook we can do following way
const [student, setStudent] = React.useState({name: 'jasper', age: 28});
setStudent((prevState) => ({
...prevState,
name: 'newName',
}));
I used this solution.
If you have a nested state like this:
this.state = {
formInputs:{
friendName:{
value:'',
isValid:false,
errorMsg:''
},
friendEmail:{
value:'',
isValid:false,
errorMsg:''
}
}
}
you can declare the handleChange function that copy current status and re-assigns it with changed values
handleChange(el) {
let inputName = el.target.name;
let inputValue = el.target.value;
let statusCopy = Object.assign({}, this.state);
statusCopy.formInputs[inputName].value = inputValue;
this.setState(statusCopy);
}
here the html with the event listener. Make sure to use the same name used into state object (in this case 'friendName')
<input type="text" onChange={this.handleChange} " name="friendName" />
try this,it should work fine
this.setState(Object.assign(this.state.jasper,{name:'someOtherName'}));
Create a state object
this.state = {
objName: {
propertyOne: "",
propertyTwo: ""
}
};
Update state using setState
this.setState(prevState => ({
objName: {
...prevState.objName,
propertyOne: "Updated Value",
propertyTwo: "Updated value"
}
}));
this is another solution using immer immutabe utility, very suited for deeply nested objects with ease, and you should not care about mutation
this.setState(
produce(draft => {
draft.jasper.name = 'someothername'
})
)
Using hooks in Functional Component:
const [state, setState] = useState({jasper: { name: 'jasper', age: 28 }})
const nameChangeHandler = () => {
setState(prevState => ({
...prevState,
prevState.jasper.name = "Anurag",
prevState.jasper.age = 28
})
)
}
In these cases It is recommended to use callback-based approach to update the state , because using this approach it is ensured that previously states are fully updated and we're updating based on previously updated state.
The first case is indeed a syntax error.
Since I can't see the rest of your component, it's hard to see why you're nesting objects in your state here. It's not a good idea to nest objects in component state. Try setting your initial state to be:
this.state = {
name: 'jasper',
age: 28
}
That way, if you want to update the name, you can just call:
this.setState({
name: 'Sean'
});
Will that achieve what you're aiming for?
For larger, more complex data stores, I would use something like Redux. But that's much more advanced.
The general rule with component state is to use it only to manage UI state of the component (e.g. active, timers, etc.)
Check out these references:
https://facebook.github.io/react/docs/react-component.html#state
https://facebook.github.io/react/docs/state-and-lifecycle.html
In case of updating an object where keys are string
e.g. let say your state object is
serviceDays: {
Sunday: true,
Monday: true,
Tuesday: false,
Wednesday: true,
Thurday: false,
Friday: true,
Saturday: true
}
so you can update in following way
const onDayClick = day => {
const { serviceDays } = this.state
this.setState(prevState => ({
serviceDays: {
...prevState.serviceDays,
[day]: serviceDays[day] ? false : true
}
}))
}
Another option: define your variable out of the Jasper object and then just call a variable.
Spread operator: ES6
this.state = { jasper: { name: 'jasper', age: 28 } }
let foo = "something that needs to be saved into state"
this.setState(prevState => ({
jasper: {
...jasper.entity,
foo
}
})
You can try with this:
this.setState(prevState => {
prevState = JSON.parse(JSON.stringify(this.state.jasper));
prevState.name = 'someOtherName';
return {jasper: prevState}
})
or for other property:
this.setState(prevState => {
prevState = JSON.parse(JSON.stringify(this.state.jasper));
prevState.age = 'someOtherAge';
return {jasper: prevState}
})
Or you can use handleChage function:
handleChage(event) {
const {name, value} = event.target;
this.setState(prevState => {
prevState = JSON.parse(JSON.stringify(this.state.jasper));
prevState[name] = value;
return {jasper: prevState}
})
}
and HTML code:
<input
type={"text"}
name={"name"}
value={this.state.jasper.name}
onChange={this.handleChange}
/>
<br/>
<input
type={"text"}
name={"age"}
value={this.state.jasper.age}
onChange={this.handleChange}
/>
You can try with this:
(Note: name of input tag === field of object)
<input name="myField" type="text"
value={this.state.myObject.myField}
onChange={this.handleChangeInpForm}>
</input>
-----------------------------------------------------------
handleChangeInpForm = (e) => {
let newObject = this.state.myObject;
newObject[e.target.name] = e.target.value;
this.setState({
myObject: newObject
})
}
Simple and dynamic way.
This will do the job, but you need to set all the ids to the parent so the parent will point to the name of the object, being id = "jasper" and name the name of the input element = property inside of the object jasper.
handleChangeObj = ({target: { id , name , value}}) => this.setState({ [id]: { ...this.state[id] , [name]: value } });
Without using Async and Await Use this...
funCall(){
this.setState({...this.state.jasper, name: 'someothername'});
}
If you using with Async And Await use this...
async funCall(){
await this.setState({...this.state.jasper, name: 'someothername'});
}
Also, following Alberto Piras solution, if you don't want to copy all the "state" object:
handleChange(el) {
let inputName = el.target.name;
let inputValue = el.target.value;
let jasperCopy = Object.assign({}, this.state.jasper);
jasperCopy[inputName].name = inputValue;
this.setState({jasper: jasperCopy});
}
Try with this:
const { jasper } = this.state; //Gets the object from state
jasper.name = 'A new name'; //do whatever you want with the object
this.setState({jasper}); //Replace the object in state
By using the input html input name attribute we can have a more dynamic approach in order to update an object properties.
DOM
html input name attribute
<input type="text" name="fname" handleChange={(e: any) => { updatePerson(e) }}/>
<input type="text" name="lname" handleChange={(e: any) => { updatePerson(e) }}/>
React / TSX
object.assign
const [person, setPerson] = useState<IPerson>({});
function updatePerson(e: React.ChangeEvent<HTMLInputElement>): void {
const { name, value } = e.currentTarget;
setPerson(prevState => {
const newState = Object.assign(person, { [name]: value })
return { ...prevState, ...newState };
});
}
Sample FC:
const [formData, setformData] = useState({
project_admin_permissions: {
task_forms: false,
auto_assign_rules: false,
project_notes: true,
alerts: false,
update_criteria: true,
project_flow: false,
reports: false,
}
})
const handleChangeCheckBox = (e) => {
setformData({
...formData, project_admin_permissions: { ...formData.project_admin_permissions, [e.target.name]: e.target.checked }
})
}
This setup worked for me:
let newState = this.state.jasper;
newState.name = 'someOtherName';
this.setState({newState: newState});
console.log(this.state.jasper.name); //someOtherName
Your second approach doesn't work because {name: 'someothername'} equals {name: 'someothername', age: undefined}, so theundefined would overwrite original age value.
When it comes to change state in nested objects, a good approach would be Immutable.js
this.state = {
jasper: Record({name: 'jasper', age: 28})
}
const {jasper} = this.state
this.setState({jasper: jasper.set(name, 'someothername')})