Related
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 a react class component that has a state object and I want to update the object with setState. I can get the state to update correctly two different ways and would like to know if one is more correct than the other.
this.state = {
people: {
name: "",
typeofComponent: "class",
}
};
onChange = e => {
// option 1
this.setState((prevState) => ({
people: {
...prevState.people, name: e.target.value
}
}));
// option 2
this.setState({ people: { name: e.target.value }});
}
Your second option would work if the state has only 1 field (name in your case). If you set that way it will overwrite the whole people. That's why we need to use spread operator inorder to make sure the other states are not lost
let a = {
people: {
name: "",
typeofComponent: "class",
}
}
let newName = 'newname'
let withSpread= {people:{...a.people,name:newName}}
let withoutSpread = {people:{name:newName}}
console.log(withSpread)
console.log(withoutSpread)
I have a form in a modal. I am trying to set states of input fields of form and when the user submits the form that data should be displayed in a table and the same form can be used to add multiple rows in a table.
I have set the initial state inside the constructor as follows
product: [{
name: '',
value:'',
price:''
}]
and on onChange I am doing the following :
changeHandler = (event) => {
console.log('change handler', event)
const value = event.target.value;
this.setState({ [event.target.name]: value
});
console.log('product : ', this.state.product)
}
The product console is empty. How can I set the state of product?
You need to update proper state item:
product: [{
name: '',
value:'',
price:''
}]
changeHandler = (event, arrayIndex) => {
const {value, name} = event.target;
const newData = this.state.product.map((el, idx) => {
if (idx === arrayIndex) {
return {
...el,
name: value
}
}
return el;
});
this.setState({product: newData});
}
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'm getting the following error, I understand what its telling me but I can't figure out how to solve the issue.
flattenChildren(...): Encountered two children with the same key...
I have 2 lists on my page which contain emails. The initial state of my app contains the following data:
const initialState = {
emails: [
{
id: 1, from: 'test.1#test.co.uk', body: 'test1 body', title: 'test 1 title',
},
{
id: 2, from: 'test.2#test.co.uk', body: 'test2 body', title: 'test 2 title',
},
],
draggedEmails: [],
};
The UI of my app lets you drag and drop items from the first list (emails) to the second list (draggedEmails).
In my Redux reducer I have the following code to move emails between the lists.
let newState = {};
//Check if the email exists in my 'emails' array
const doesExistInEmails = state.emails.find(x => x.id === action.id) !== null;
//If it exists then move it to the 'draggedEmails' list
if (doesExistInEmails) {
const filteredEmails = state.emails.filter(e => e.id !== action.emailItem.id);
newState = Object.assign(
{},
state,
{ draggedEmails: [...state.draggedEmails, action.emailItem], emails: filteredEmails }
);
} else {
const filteredEmails = state.emails.filter(e => e.id !== action.emailItem.id);
newState = Object.assign(
{},
state,
{ draggedEmails: [...state.emails, action.emailItem], emails: filteredEmails });
}
return newState;
The problem occurs when I move the items BACK to the emails list, once they have been moved to the 'draggedEmails' list.
The following code is what is used to create the elements and the keys.
createEmailItem(em) {
return React.createElement(
EmailItem, { email: em, key: `${em.id}` });
}
Any help is appreciated,
Thanks.
EDIT: Console.Logged state after moving one item from the 'emails' list to the 'draggedEmails' list. Everything looks as it should.
Object {emails: Array[1], draggedEmails: Array[1]}
EDIT2: Adding render method.
render() {
return (
<div className="email-container" onDrop={this.onDrop} onDragOver={this.allowDrop}>
{this.props.emails.map(this.createEmailItem)}
</div>
);
}
I found the problem. There were 4.
The first is that the following was returning 'undefined' rather than 'null'
const doesExistInEmails = state.emails.find(x => x.id === action.id) !== null;
The second is that my action doesn't have an id, my action has an emailItem which has an id
const doesExistInEmails = state.emails.find(x => x.id === action.emailItem.id) !== undefined;
The third is that I was filtering my emails rather than dragged emails in the following line.
const filteredEmails = state.filter(e => e.id !== action.emailItem.id);
And finally I was assigning the wrong values back when setting the state.
{ draggedEmails: [...state.emails, action.emailItem], emails: filteredEmails });
Should be...
{ emails: [...state.emails, action.emailItem], draggedEmails: filteredEmails });
So overall, I had lots wrong...
Thanks to the guys who commented.