Select option value not equal when change value [duplicate] - javascript

So I have this:
let total = newDealersDeckTotal.reduce(function(a, b) {
return a + b;
},
0);
console.log(total, 'tittal'); //outputs correct total
setTimeout(() => {
this.setState({ dealersOverallTotal: total });
}, 10);
console.log(this.state.dealersOverallTotal, 'dealersOverallTotal1'); //outputs incorrect total
newDealersDeckTotal is just an array of numbers [1, 5, 9] e.g.
however this.state.dealersOverallTotal does not give the correct total but total does? I even put in a timeout delay to see if this solved the problem.
any obvious or should I post more code?

setState() is usually asynchronous, which means that at the time you console.log the state, it's not updated yet. Try putting the log in the callback of the setState() method. It is executed after the state change is complete:
this.setState({ dealersOverallTotal: total }, () => {
console.log(this.state.dealersOverallTotal, 'dealersOverallTotal1');
});

In case of hooks, you should use useEffect hook.
const [fruit, setFruit] = useState('');
setFruit('Apple');
useEffect(() => {
console.log('Fruit', fruit);
}, [fruit])

setState is asynchronous. You can use callback method to get updated state.
changeHandler(event) {
this.setState({ yourName: event.target.value }, () =>
console.log(this.state.yourName));
}

Using async/await
async changeHandler(event) {
await this.setState({ yourName: event.target.value });
console.log(this.state.yourName);
}

The setState is asynchronous in react, so to see the updated state in console use the callback as shown below (Callback function will execute after the setState update)
this.setState({ email: 'test#example.com' }, () => {
console.log(this.state.email)
)}

I had an issue when setting react state multiple times (it always used default state). Following this react/github issue worked for me
const [state, setState] = useState({
foo: "abc",
bar: 123
});
// Do this!
setState(prevState => {
return {
...prevState,
foo: "def"
};
});
setState(prevState => {
return {
...prevState,
bar: 456
};
});

The setState() operation is asynchronous and hence your console.log() will be executed before the setState() mutates the values and hence you see the result.
To solve it, log the value in the callback function of setState(), like:
setTimeout(() => {
this.setState({dealersOverallTotal: total},
function(){
console.log(this.state.dealersOverallTotal, 'dealersOverallTotal1');
});
}, 10)

If you work with funcions you need to use UseEffect to deal with setState's asynchrony (you can't use the callback as you did when working with classes). An example:
import { useState, useEffect } from "react";
export default function App() {
const [animal, setAnimal] = useState(null);
function changeAnimal(newAnimal) {
setAnimal(newAnimal);
// here 'animal' is not what you would expect
console.log("1", animal);
}
useEffect(() => {
if (animal) {
console.log("2", animal);
}
}, [animal]);
return (
<div className="App">
<button onClick={() => changeAnimal("dog")} />
</div>
);
}
First console.log returns null, and the second one returns 'dog'

just add componentDidUpdate(){} method in your code, and it will work.
you can check the life cycle of react native here:
https://images.app.goo.gl/BVRAi4ea2P4LchqJ8

As well as noting the asynchronous nature of setState, be aware that you may have competing event handlers, one doing the state change you want and the other immediately undoing it again. For example onClick on a component whose parent also handles the onClick. Check by adding trace. Prevent this by using e.stopPropagation.

I had the same situation with some convoluted code, and nothing from the existing suggestions worked for me.
My problem was that setState was happening from callback func, issued by one of the components. And my suspicious is that the call was occurring synchronously, which prevented setState from setting state at all.
Simply put I have something like this:
render() {
<Control
ref={_ => this.control = _}
onChange={this.handleChange}
onUpdated={this.handleUpdate} />
}
handleChange() {
this.control.doUpdate();
}
handleUpdate() {
this.setState({...});
}
The way I had to "fix" it was to put doUpdate() into setTimeout like this:
handleChange() {
setTimeout(() => { this.control.doUpdate(); }, 10);
}
Not ideal, but otherwise it would be a significant refactoring.

Related

useState in React Native fails to mount new value? [duplicate]

So I have this:
let total = newDealersDeckTotal.reduce(function(a, b) {
return a + b;
},
0);
console.log(total, 'tittal'); //outputs correct total
setTimeout(() => {
this.setState({ dealersOverallTotal: total });
}, 10);
console.log(this.state.dealersOverallTotal, 'dealersOverallTotal1'); //outputs incorrect total
newDealersDeckTotal is just an array of numbers [1, 5, 9] e.g.
however this.state.dealersOverallTotal does not give the correct total but total does? I even put in a timeout delay to see if this solved the problem.
any obvious or should I post more code?
setState() is usually asynchronous, which means that at the time you console.log the state, it's not updated yet. Try putting the log in the callback of the setState() method. It is executed after the state change is complete:
this.setState({ dealersOverallTotal: total }, () => {
console.log(this.state.dealersOverallTotal, 'dealersOverallTotal1');
});
In case of hooks, you should use useEffect hook.
const [fruit, setFruit] = useState('');
setFruit('Apple');
useEffect(() => {
console.log('Fruit', fruit);
}, [fruit])
setState is asynchronous. You can use callback method to get updated state.
changeHandler(event) {
this.setState({ yourName: event.target.value }, () =>
console.log(this.state.yourName));
}
Using async/await
async changeHandler(event) {
await this.setState({ yourName: event.target.value });
console.log(this.state.yourName);
}
The setState is asynchronous in react, so to see the updated state in console use the callback as shown below (Callback function will execute after the setState update)
this.setState({ email: 'test#example.com' }, () => {
console.log(this.state.email)
)}
I had an issue when setting react state multiple times (it always used default state). Following this react/github issue worked for me
const [state, setState] = useState({
foo: "abc",
bar: 123
});
// Do this!
setState(prevState => {
return {
...prevState,
foo: "def"
};
});
setState(prevState => {
return {
...prevState,
bar: 456
};
});
The setState() operation is asynchronous and hence your console.log() will be executed before the setState() mutates the values and hence you see the result.
To solve it, log the value in the callback function of setState(), like:
setTimeout(() => {
this.setState({dealersOverallTotal: total},
function(){
console.log(this.state.dealersOverallTotal, 'dealersOverallTotal1');
});
}, 10)
If you work with funcions you need to use UseEffect to deal with setState's asynchrony (you can't use the callback as you did when working with classes). An example:
import { useState, useEffect } from "react";
export default function App() {
const [animal, setAnimal] = useState(null);
function changeAnimal(newAnimal) {
setAnimal(newAnimal);
// here 'animal' is not what you would expect
console.log("1", animal);
}
useEffect(() => {
if (animal) {
console.log("2", animal);
}
}, [animal]);
return (
<div className="App">
<button onClick={() => changeAnimal("dog")} />
</div>
);
}
First console.log returns null, and the second one returns 'dog'
just add componentDidUpdate(){} method in your code, and it will work.
you can check the life cycle of react native here:
https://images.app.goo.gl/BVRAi4ea2P4LchqJ8
As well as noting the asynchronous nature of setState, be aware that you may have competing event handlers, one doing the state change you want and the other immediately undoing it again. For example onClick on a component whose parent also handles the onClick. Check by adding trace. Prevent this by using e.stopPropagation.
I had the same situation with some convoluted code, and nothing from the existing suggestions worked for me.
My problem was that setState was happening from callback func, issued by one of the components. And my suspicious is that the call was occurring synchronously, which prevented setState from setting state at all.
Simply put I have something like this:
render() {
<Control
ref={_ => this.control = _}
onChange={this.handleChange}
onUpdated={this.handleUpdate} />
}
handleChange() {
this.control.doUpdate();
}
handleUpdate() {
this.setState({...});
}
The way I had to "fix" it was to put doUpdate() into setTimeout like this:
handleChange() {
setTimeout(() => { this.control.doUpdate(); }, 10);
}
Not ideal, but otherwise it would be a significant refactoring.

React understanding hooks and how to set the state [duplicate]

So I have this:
let total = newDealersDeckTotal.reduce(function(a, b) {
return a + b;
},
0);
console.log(total, 'tittal'); //outputs correct total
setTimeout(() => {
this.setState({ dealersOverallTotal: total });
}, 10);
console.log(this.state.dealersOverallTotal, 'dealersOverallTotal1'); //outputs incorrect total
newDealersDeckTotal is just an array of numbers [1, 5, 9] e.g.
however this.state.dealersOverallTotal does not give the correct total but total does? I even put in a timeout delay to see if this solved the problem.
any obvious or should I post more code?
setState() is usually asynchronous, which means that at the time you console.log the state, it's not updated yet. Try putting the log in the callback of the setState() method. It is executed after the state change is complete:
this.setState({ dealersOverallTotal: total }, () => {
console.log(this.state.dealersOverallTotal, 'dealersOverallTotal1');
});
In case of hooks, you should use useEffect hook.
const [fruit, setFruit] = useState('');
setFruit('Apple');
useEffect(() => {
console.log('Fruit', fruit);
}, [fruit])
setState is asynchronous. You can use callback method to get updated state.
changeHandler(event) {
this.setState({ yourName: event.target.value }, () =>
console.log(this.state.yourName));
}
Using async/await
async changeHandler(event) {
await this.setState({ yourName: event.target.value });
console.log(this.state.yourName);
}
The setState is asynchronous in react, so to see the updated state in console use the callback as shown below (Callback function will execute after the setState update)
this.setState({ email: 'test#example.com' }, () => {
console.log(this.state.email)
)}
I had an issue when setting react state multiple times (it always used default state). Following this react/github issue worked for me
const [state, setState] = useState({
foo: "abc",
bar: 123
});
// Do this!
setState(prevState => {
return {
...prevState,
foo: "def"
};
});
setState(prevState => {
return {
...prevState,
bar: 456
};
});
The setState() operation is asynchronous and hence your console.log() will be executed before the setState() mutates the values and hence you see the result.
To solve it, log the value in the callback function of setState(), like:
setTimeout(() => {
this.setState({dealersOverallTotal: total},
function(){
console.log(this.state.dealersOverallTotal, 'dealersOverallTotal1');
});
}, 10)
If you work with funcions you need to use UseEffect to deal with setState's asynchrony (you can't use the callback as you did when working with classes). An example:
import { useState, useEffect } from "react";
export default function App() {
const [animal, setAnimal] = useState(null);
function changeAnimal(newAnimal) {
setAnimal(newAnimal);
// here 'animal' is not what you would expect
console.log("1", animal);
}
useEffect(() => {
if (animal) {
console.log("2", animal);
}
}, [animal]);
return (
<div className="App">
<button onClick={() => changeAnimal("dog")} />
</div>
);
}
First console.log returns null, and the second one returns 'dog'
just add componentDidUpdate(){} method in your code, and it will work.
you can check the life cycle of react native here:
https://images.app.goo.gl/BVRAi4ea2P4LchqJ8
As well as noting the asynchronous nature of setState, be aware that you may have competing event handlers, one doing the state change you want and the other immediately undoing it again. For example onClick on a component whose parent also handles the onClick. Check by adding trace. Prevent this by using e.stopPropagation.
I had the same situation with some convoluted code, and nothing from the existing suggestions worked for me.
My problem was that setState was happening from callback func, issued by one of the components. And my suspicious is that the call was occurring synchronously, which prevented setState from setting state at all.
Simply put I have something like this:
render() {
<Control
ref={_ => this.control = _}
onChange={this.handleChange}
onUpdated={this.handleUpdate} />
}
handleChange() {
this.control.doUpdate();
}
handleUpdate() {
this.setState({...});
}
The way I had to "fix" it was to put doUpdate() into setTimeout like this:
handleChange() {
setTimeout(() => { this.control.doUpdate(); }, 10);
}
Not ideal, but otherwise it would be a significant refactoring.

React useState Updating Issues [duplicate]

So I have this:
let total = newDealersDeckTotal.reduce(function(a, b) {
return a + b;
},
0);
console.log(total, 'tittal'); //outputs correct total
setTimeout(() => {
this.setState({ dealersOverallTotal: total });
}, 10);
console.log(this.state.dealersOverallTotal, 'dealersOverallTotal1'); //outputs incorrect total
newDealersDeckTotal is just an array of numbers [1, 5, 9] e.g.
however this.state.dealersOverallTotal does not give the correct total but total does? I even put in a timeout delay to see if this solved the problem.
any obvious or should I post more code?
setState() is usually asynchronous, which means that at the time you console.log the state, it's not updated yet. Try putting the log in the callback of the setState() method. It is executed after the state change is complete:
this.setState({ dealersOverallTotal: total }, () => {
console.log(this.state.dealersOverallTotal, 'dealersOverallTotal1');
});
In case of hooks, you should use useEffect hook.
const [fruit, setFruit] = useState('');
setFruit('Apple');
useEffect(() => {
console.log('Fruit', fruit);
}, [fruit])
setState is asynchronous. You can use callback method to get updated state.
changeHandler(event) {
this.setState({ yourName: event.target.value }, () =>
console.log(this.state.yourName));
}
Using async/await
async changeHandler(event) {
await this.setState({ yourName: event.target.value });
console.log(this.state.yourName);
}
The setState is asynchronous in react, so to see the updated state in console use the callback as shown below (Callback function will execute after the setState update)
this.setState({ email: 'test#example.com' }, () => {
console.log(this.state.email)
)}
I had an issue when setting react state multiple times (it always used default state). Following this react/github issue worked for me
const [state, setState] = useState({
foo: "abc",
bar: 123
});
// Do this!
setState(prevState => {
return {
...prevState,
foo: "def"
};
});
setState(prevState => {
return {
...prevState,
bar: 456
};
});
The setState() operation is asynchronous and hence your console.log() will be executed before the setState() mutates the values and hence you see the result.
To solve it, log the value in the callback function of setState(), like:
setTimeout(() => {
this.setState({dealersOverallTotal: total},
function(){
console.log(this.state.dealersOverallTotal, 'dealersOverallTotal1');
});
}, 10)
If you work with funcions you need to use UseEffect to deal with setState's asynchrony (you can't use the callback as you did when working with classes). An example:
import { useState, useEffect } from "react";
export default function App() {
const [animal, setAnimal] = useState(null);
function changeAnimal(newAnimal) {
setAnimal(newAnimal);
// here 'animal' is not what you would expect
console.log("1", animal);
}
useEffect(() => {
if (animal) {
console.log("2", animal);
}
}, [animal]);
return (
<div className="App">
<button onClick={() => changeAnimal("dog")} />
</div>
);
}
First console.log returns null, and the second one returns 'dog'
just add componentDidUpdate(){} method in your code, and it will work.
you can check the life cycle of react native here:
https://images.app.goo.gl/BVRAi4ea2P4LchqJ8
As well as noting the asynchronous nature of setState, be aware that you may have competing event handlers, one doing the state change you want and the other immediately undoing it again. For example onClick on a component whose parent also handles the onClick. Check by adding trace. Prevent this by using e.stopPropagation.
I had the same situation with some convoluted code, and nothing from the existing suggestions worked for me.
My problem was that setState was happening from callback func, issued by one of the components. And my suspicious is that the call was occurring synchronously, which prevented setState from setting state at all.
Simply put I have something like this:
render() {
<Control
ref={_ => this.control = _}
onChange={this.handleChange}
onUpdated={this.handleUpdate} />
}
handleChange() {
this.control.doUpdate();
}
handleUpdate() {
this.setState({...});
}
The way I had to "fix" it was to put doUpdate() into setTimeout like this:
handleChange() {
setTimeout(() => { this.control.doUpdate(); }, 10);
}
Not ideal, but otherwise it would be a significant refactoring.

React component state only changes in DevTools hooks not in front or console.logs [duplicate]

So I have this:
let total = newDealersDeckTotal.reduce(function(a, b) {
return a + b;
},
0);
console.log(total, 'tittal'); //outputs correct total
setTimeout(() => {
this.setState({ dealersOverallTotal: total });
}, 10);
console.log(this.state.dealersOverallTotal, 'dealersOverallTotal1'); //outputs incorrect total
newDealersDeckTotal is just an array of numbers [1, 5, 9] e.g.
however this.state.dealersOverallTotal does not give the correct total but total does? I even put in a timeout delay to see if this solved the problem.
any obvious or should I post more code?
setState() is usually asynchronous, which means that at the time you console.log the state, it's not updated yet. Try putting the log in the callback of the setState() method. It is executed after the state change is complete:
this.setState({ dealersOverallTotal: total }, () => {
console.log(this.state.dealersOverallTotal, 'dealersOverallTotal1');
});
In case of hooks, you should use useEffect hook.
const [fruit, setFruit] = useState('');
setFruit('Apple');
useEffect(() => {
console.log('Fruit', fruit);
}, [fruit])
setState is asynchronous. You can use callback method to get updated state.
changeHandler(event) {
this.setState({ yourName: event.target.value }, () =>
console.log(this.state.yourName));
}
Using async/await
async changeHandler(event) {
await this.setState({ yourName: event.target.value });
console.log(this.state.yourName);
}
The setState is asynchronous in react, so to see the updated state in console use the callback as shown below (Callback function will execute after the setState update)
this.setState({ email: 'test#example.com' }, () => {
console.log(this.state.email)
)}
I had an issue when setting react state multiple times (it always used default state). Following this react/github issue worked for me
const [state, setState] = useState({
foo: "abc",
bar: 123
});
// Do this!
setState(prevState => {
return {
...prevState,
foo: "def"
};
});
setState(prevState => {
return {
...prevState,
bar: 456
};
});
The setState() operation is asynchronous and hence your console.log() will be executed before the setState() mutates the values and hence you see the result.
To solve it, log the value in the callback function of setState(), like:
setTimeout(() => {
this.setState({dealersOverallTotal: total},
function(){
console.log(this.state.dealersOverallTotal, 'dealersOverallTotal1');
});
}, 10)
If you work with funcions you need to use UseEffect to deal with setState's asynchrony (you can't use the callback as you did when working with classes). An example:
import { useState, useEffect } from "react";
export default function App() {
const [animal, setAnimal] = useState(null);
function changeAnimal(newAnimal) {
setAnimal(newAnimal);
// here 'animal' is not what you would expect
console.log("1", animal);
}
useEffect(() => {
if (animal) {
console.log("2", animal);
}
}, [animal]);
return (
<div className="App">
<button onClick={() => changeAnimal("dog")} />
</div>
);
}
First console.log returns null, and the second one returns 'dog'
just add componentDidUpdate(){} method in your code, and it will work.
you can check the life cycle of react native here:
https://images.app.goo.gl/BVRAi4ea2P4LchqJ8
As well as noting the asynchronous nature of setState, be aware that you may have competing event handlers, one doing the state change you want and the other immediately undoing it again. For example onClick on a component whose parent also handles the onClick. Check by adding trace. Prevent this by using e.stopPropagation.
I had the same situation with some convoluted code, and nothing from the existing suggestions worked for me.
My problem was that setState was happening from callback func, issued by one of the components. And my suspicious is that the call was occurring synchronously, which prevented setState from setting state at all.
Simply put I have something like this:
render() {
<Control
ref={_ => this.control = _}
onChange={this.handleChange}
onUpdated={this.handleUpdate} />
}
handleChange() {
this.control.doUpdate();
}
handleUpdate() {
this.setState({...});
}
The way I had to "fix" it was to put doUpdate() into setTimeout like this:
handleChange() {
setTimeout(() => { this.control.doUpdate(); }, 10);
}
Not ideal, but otherwise it would be a significant refactoring.

React useEffect executing last function

I need to have 2 different functions that update 2 different components only once in the beginning. Hence, I'm using useEffect. The code is as follows
const loadCategories = () => {
getCategories().then((c) => setValues({ ...values, categories: c.data }));
}
const loadStores = () => {
getStores().then((c) => setValues({ ...values, stores: c.data }));
}
useEffect(() => {
loadStores();
loadCategories();
}, []);
Both the functions are setting the values of the dropdown elements
The problem is though both functions are exectued, only loadCategories() function logic is reflected in the UI. How to make both functions logic reflect in the UI?
first better practice to add those function in useEffect or to wrap them in useCallback hook.
second both or your function are promises so each may not resolve at same time and when you trying to update state values will keep it initial value that why your first function is not reflecting in the ui instead use setState callback to get the previous state like this :
useEffect(() => {
const loadCategories = () => {
getCategories().then((c) => setValues(prevState=>({ ...prevState, categories: c.data })));
}
const loadStores = () => {
getStores().then((c) => setValues(prevState=>({ ...prevState, stores: c.data })));
}
loadStores();
loadCategories();
}, []);
Promise and useEffect can be challenging as the component might dismount before you promise is full-filled.
Here is a solution which works quite well:
useEffect(() => {
let isRunning = true;
Promise.all([
getCategories(),
getStores()
]).then(([stores, categories]) => {
// Stop if component was unmounted:
if (!isRunning) { return }
// Do anything you like with your lazy load values:
console.log(stores, categories)
});
return () => {
isRunning = false;
}
}, []);
Wait for both promises to resolve and then use the data from both to update your state, combined in whatever way you see fit.
useEffect(() => {
Promise.all([getCategories(), getStores()]).then(([categories, stores]) => {
setValues({categories, stores})
});
}, []);
The problem with what you had before (as you experienced) is that values is always the value at the point at which useState was run on this render.
If you really want to do the updates separately, than you can look into useReducer: https://reactjs.org/docs/hooks-reference.html#usereducer
You are lying to React about dependencies. Both your functions depend on the values state variable. That's also why it does not work: When the hooks get run, values gets closured, then when setValues runs values changes (gets set to a new object), however inside the closure it is still referencing the old values.
You can easily resolve that by passing a callback to setValues, this way you do not have a dependency to the outside and the values update is atomic:
setValues(values => ({ ...values, stores: c.data }));

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