Develop Reference

Can't update multiple state properties at the same time on my React App

I do this project from this course and I want to increase the possibilities of the app by giving the user the ability to insert a birthday person by putting the name, age and photo with a HTML form. In order to do so i use this:
import React, { useState } from 'react'
import ReactDOM from 'react-dom'
class MyForm extends React.Component {
constructor(props) {
super(props)
this.state = {
username: '',
age: null,
filename: null,
}
}
myChangeHandler = (event) => {
event.nativeEvent.stopImmediatePropagation()
let nam = event.target.name
let val = event.target.value
console.log('click')
if (nam === 'age') {
if (!Number(val)) {
alert('Your age must be a number')
}
}
this.setState({
[nam]: val,
file: URL.createObjectURL(event.target.files[0]),
})
}
render() {
return (
<div className="form">
<form>
<h1 className="title">
Today is the Birtday of {this.state.username} of {this.state.age}{' '}
Years Old
</h1>
<img src={this.state.file} alt="Birtday Pic" />
<p>Enter the name of the Birtday Person:</p>
<input type="text" name="username" onChange={this.myChangeHandler} />
<p>Enter his/her age:</p>
<input type="text" name="age" onChange={this.myChangeHandler} />
<p>Click on the chosen button to send the birtday pic</p>
<input
type="file"
id="myFile"
name="filename"
onChange={this.myChangeHandler}
></input>
<button
type="button"
onClick={() => document.getElementById('myFile').click()}
className="send"
>
Send the Birtday Picture
</button>
<input type="submit" value="Submit"></input>
</form>
</div>
)
}
}
export default MyForm
But here is the issue,I can insert the image but when I tring to put name or age this happends:
I am just a rookie with React, maybe this is some silly thing, maybe I don't use well setState(), but I can't see the issue right now

You're using the same setState for every change:
this.setState({
[nam]: val,
file: URL.createObjectURL(event.target.files[0]),
})
HOWEVER, not every event will have .files - only the change handler used by the file input.
I would make a separate change handler for the file input. Have one for text inputs, and one for file inputs.
For example, for file inputs:
myFileChangeHandler = (event) => {
event.nativeEvent.stopImmediatePropagation()
let nam = event.target.name
let val = event.target.value
this.setState({
[nam]: val,
file: URL.createObjectURL(event.target.files[0]),
})
}
and this for text inputs:
myTextChangeHandler = (event) => {
event.nativeEvent.stopImmediatePropagation()
let nam = event.target.name
let val = event.target.value
if (nam === 'age') {
if (!Number(val)) {
alert('Your age must be a number')
}
}
this.setState({
[nam]: val,
})
}

I am facing a problem in JavaScript/ReactJS

I am working in ReactJS on post API. I have given a task to create some text fields in which I have to give some values and then on click of a submit button the information from text field will be submitted to POST API which I have taken from JasonPlaceHolder.
I have written a code which is given at last. Whenever I click Register button the value in last input field (which in my case is "EMAIL") overrides the values of all the input fields.
A screenshot of my problem is also attached:
Code
import React from 'react';
import logo from './logo.svg';
import './App.css';
import axios from 'axios';
class App extends React.Component {
constructor(props){
super(props);
this.state = {
error: null,
isLoaded: false,
items: [],
inter:0,
ID: '',
Name: '',
username : '',
Email: ''
};
this.updateInput = this.updateInput.bind(this);
this.handleSubmit = this.handleSubmit.bind(this);
}
updateInput(event){
this.setState({ID : event.target.value})
this.setState({Name : event.target.value})
this.setState({username : event.target.value})
this.setState({Email : event.target.value})
}
handleSubmit(){
var dict = { id: this.state.ID, name:this.state.Name , username: this.state.username , email: this.state.Email };
axios.post('https://jsonplaceholder.typicode.com/users', dict)
.then(response => {
console.log(response)
this.setState({isLoaded:true,
flag:1,
})
})
.catch(error => {
alert(error);
console.log(error);
})
}
render() {
const { error, isLoaded, items } = this.state;
if (this.state.inter == 0){
return(
<div>
<form>
<p>ID:<input type="text" name="ID" onChange={this.updateInput}/> </p>
<p>Name:<input type="text" name="name" onChange={this.updateInput} /> </p>
<p>User Name:<input type="text" name="username" onChange={this.updateInput} /></p>
<p>Email: <input type="text" name="email" onChange={this.updateInput} /></p>
</form>
<button onClick={this.handleSubmit}>
Register
</button>
</div>
);
}else{
return(
<div>
<button onClick={this.handleSubmit} >
Register
</button>
<h1> Post Request Submitted Successfully</h1>
</div>
);
}
}
componentDidMount() {
}
}
export default App;

Your updateInput method overrides all the other fields, that's why the last updated field (the email) is the one you are seeing on the request payload.
To solve this you can separate the updateInput method for each input field or inside updateInput check which field you're currently updating and update only that field.
You can check here for more details:
https://medium.com/#zacjones/handle-multiple-inputs-in-react-with-es6-computed-property-name-e3d41861ae46

You have to update the fields like this,
updateInput({target: {name, value}}){
this.setState({[name]: value});
}

The issue is in the updateInput method. change it to.
const { name, value } = event.target;
this.setState(state => ({
...state, [name]: value,
}));
N:B You will have to make the names of the input element same as the state field.

Change your updateInput logic to this.
updateInput(event){
this.setState({[event.target.name] : event.target.value})
}

Value of this is undefined

I have a this value inside an if statement, nested inside a my handleFormChange function. I've tried to use arrow functions with this function to bind the value of this but im getting the following error message:
TypeError: Cannot set property 'author' of undefined
From my understanding usually you find the this value by looking at where the function containing this is called. However, in my case im struggling to work this out. Can anyone explain to me why it is undefined and how to solve this issue? Here is the code:
class CommentForm extends React.Component{
constructor(props){
super(props)
var comment={author:'', message:''}
}
handleSubmit= (e)=>{
e.preventDefault()
var authorVal = this.comment.author;
var textVal = this.comment.message;
//this stops any comment submittal if anything missing
if (!textVal || !authorVal) {
return;
}
this.props.onCommentSubmit(this.comment);
//reset form values
e.target[0].value = '';
e.target[1].value = '';
return;
}
handleFormChange= (e)=>{
e.preventDefault()
if(e.target.name==='author'){
var author = e.target.value.trim();
this.comment.author = author
}else if(e.target.name==='message'){
var message = e.target.value.trim();
this.comment.message = message
}
}
render() {
return (
<form className = "ui form" method="post" onChange={(e)=>{this.handleFormChange(e)}} onSubmit={(e)=>{this.handleSubmit(e)}}>
<div className="form-group">
<input
className="form-control"
placeholder="user..."
name="author"
type="text"
/>
</div>
<div className="form-group">
<textarea
className="form-control"
placeholder="comment..."
name="message"
/>
</div>
<div className="form-group">
<button disabled={null} className="btn btn-primary">
Comment ➤
</button>
</div>
</form>
);
}
}
export default CommentForm

The first step into learning how to do what you want is to study how React's State works (official docs are great at explaning it).
This example is not complete, but should guide you through the proccess.
class CommentForm extends Component {
constructor(props) {
super(props);
this.state = {
author : '',
message : '',
}
this.onChangeAuthorName = this.onChangeAuthorName.bind(this);
this.onBlurAuthorName = this.onBlurAuthorName.bind(this);
}
onChangeAuthorName(e) {
this.setState({ author: e.target.value });
}
onBlurAuthorName() {
// trim on blur (or when you send to the network, to avoid
// having the user not being able to add empty whitespaces
// while typing
this.setState({ author: this.state.author.trim() })
}
render() {
return (
...
<input value={this.state.author} onChange={this.onChangeAuthorName} onBlur={this.onBlurAuthorName} />
...
);
}
}
Usually, when you want to "set" variables in React, you don't add them as you do to in Javascript classes (this.comment = e.target.value), but instead, use the function setState(). From the docs:
// Wrong
this.state.comment = 'Hello';
Instead, use setState():
// Correct
this.setState({comment: 'Hello'});
(NOTE: Alternatively, this could be done using React Hooks, but I recommend you learn the lifecycle methods firsthand. Good luck!)

I decided to write even if you proposed the correct answer for the simple reason that I think my code is closer to what it published.
import React, { Component } from "react";
import ReactDOM from "react-dom";
class App extends Component {
constructor(props) {
super(props);
this.state = {
comment: {},
some: 1
};
}
handleFormChange = e => {
e.preventDefault();
let { comment } = this.state;
const newCommentState = function() {
let returnObj = { ...comment };
returnObj[this.target.name] = this.target.value.trim();
return returnObj;
}.bind(e)();
this.setState({ comment: newCommentState });
};
handleSubmit = e => {
e.preventDefault();
let { comment } = this.state;
if (!comment.author || !comment.message) return;
this.props.onCommentSubmit(comment);
this.setState({ comment: {} });
e.target[0].value = "";
e.target[1].value = "";
};
render() {
return (
<div>
<form
className="ui form"
method="post"
onChange={e => {
this.handleFormChange(e);
}}
onSubmit={e => {
this.handleSubmit(e);
}}
>
<div className="form-group">
<input
className="form-control"
placeholder="user..."
name="author"
type="text"
/>
</div>
<div className="form-group">
<textarea
className="form-control"
placeholder="comment..."
name="message"
/>
</div>
<div className="form-group">
<button disabled={null} className="btn btn-primary">
Comment ➤
</button>
</div>
</form>
</div>
);
}
}
const rootElement = document.getElementById("root");
ReactDOM.render(<App />, rootElement);
Live example:

Unable to type into React input field

I am unable to type any input into my input field. I am using React, and have already set a handleChange and a handleSubmit function. The first two input fields, for 'name' and 'email', take input just fine. But for 'favoriteCity', it doesn't seem to work.
I am wondering if it is due to a MongoDB error that I am getting.
class UserPage extends Component {
state = {
user: [],
newUser: {
name: '',
email: '',
favoriteCity: ''
}
}
getAllUsers = () => {
axios.get('/api/users')
.then(res => {
this.setState({ user: res.data })
})
}
componentDidMount() {
this.getAllUsers()
}
handleChange = event => {
const newUser = { ...this.state.newUser };
newUser[event.target.name] = event.target.value;
this.setState({ newUser: newUser});
}
handleSubmit = event => {
event.preventDefault()
axios.post('/api/users', this.state.newUser)
.then(res => {
this.props.history.push(`/users/${res.data._id}`)
})
}
render() {
return (
<div>
{ /* This shows a list of All Users */ }
{this.state.user.map(user => (
<div key={user._id}>
<Link to={`/users/${user._id}`}>{user.name}</Link>
</div>
))}
<h1>New User Page</h1>
<form onSubmit={this.handleSubmit}>
<label>Name: </label>
<input
type="text"
name="name"
placeholder="Name?"
value={this.state.newUser.name}
onChange={this.handleChange}
/>
<label>Email: </label>
<input
type="text"
name="email"
placeholder="Email?"
value={this.state.newUser.email}
onChange={this.handleChange}
/>
<label>Favorite City: </label>
<input
type="text"
name="city"
placeholder="Favorite City?"
value={this.state.newUser.favoriteCity}
onChange={this.handleChange}
/>
<Button
type="submit"
value="Submit"
variant="contained"
color="primary"
>
Create User
</Button>
</form>
</div>
);
}
}
export default UserPage;
Please help.

Weird that email works fine, from what you posted your handleChange function is only updating the name on the newUser.
What you should see is what you type in all the inputs appear in the name input.
To fix this, you should probably have separate change handlers for each input:
handleNameChange
handleEmailChange
...
You should also consider storing name, email etc.. at the root of your state instead of nesting them in an object, that'll simplify the handler functions code.

How do I edit multiple input controlled components in React?

I have a component that stores a contact object as state - {firstName: "John", lastName: "Doe", phone: "1234567890} I want to create a form to edit this object but if I want the inputs to hold the value of the original contact parameter, I need to make each input a controlled component. However, I don't know how to create a handleChange function that will adjust to each parameter because my state only holds {contact: {...}}. Below is what I currently have -
getInitialState: function () {
return ({contact: {}});
},
handleChange: function (event) {
this.setState({contact: event.target.value });
},
render: function () {
return (
<div>
<input type="text" onChange={this.handleChange} value={this.state.contact.firstName}/>
<input type="text" onChange={this.handleChange} value={this.state.contact.lastName}/>
<input type="text" onChange={this.handleChange} value={this.state.contact.lastName}/>
</div>
);
}
I wish in my handleChange I can do something like
handleChange: function (event) {
this.setState({contact.firstName: event.target.value });
}

There's a "simple" way to do this, and a "smart" way. If you ask me, doing things the smart way is not always the best, because I may be harder to work with later. In this case, both are quite understandable.
Side note: One thing I'd ask you to think about, is do you need to update the contact object, or could you just keep firstName etc. directly on state? Maybe you have a lot of data in the state of the component? If that is the case, it's probably a good idea to separate it into smaller components with narrower responsibilities.
The "simple" way
changeFirstName: function (event) {
const contact = this.state.contact;
contact.firstName = event.target.value;
this.setState({ contact: contact });
},
changeLastName: function (event) {
const contact = this.state.contact;
contact.lastName = event.target.value;
this.setState({ contact: contact });
},
changePhone: function (event) {
const contact = this.state.contact;
contact.phone = event.target.value;
this.setState({ contact: contact });
},
render: function () {
return (
<div>
<input type="text" onChange={this.changeFirstName.bind(this)} value={this.state.contact.firstName}/>
<input type="text" onChange={this.changeLastName.bind(this)} value={this.state.contact.lastName}/>
<input type="text" onChange={this.changePhone.bind(this)} value={this.state.contact.phone}/>
</div>
);
}
The "smart" way
handleChange: function (propertyName, event) {
const contact = this.state.contact;
contact[propertyName] = event.target.value;
this.setState({ contact: contact });
},
render: function () {
return (
<div>
<input type="text" onChange={this.handleChange.bind(this, 'firstName')} value={this.state.contact.firstName}/>
<input type="text" onChange={this.handleChange.bind(this, 'lastName')} value={this.state.contact.lastName}/>
<input type="text" onChange={this.handleChange.bind(this, 'phone')} value={this.state.contact.lastName}/>
</div>
);
}
Update: Same examples using ES2015+
This section contains the same examples as shown above, but using features from ES2015+.
To support the following features across browsers you need to transpile your code with Babel using e.g.
the presets es2015 and react,
and the plugin stage-0.
Below are updated examples, using object destructuring to get the contact from the state,
spread operator to
create an updated contact object instead of mutating the existing one,
creating components as Classes by
extending React.Component,
and using arrow funtions to
create callbacks so we don't have to bind(this).
The "simple" way, ES2015+
class ContactEdit extends React.Component {
changeFirstName = (event) => {
const { contact } = this.state;
const newContact = {
...contact,
firstName: event.target.value
};
this.setState({ contact: newContact });
}
changeLastName = (event) => {
const { contact } = this.state;
const newContact = {
...contact,
lastName: event.target.value
};
this.setState({ contact: newContact });
}
changePhone = (event) => {
const { contact } = this.state;
const newContact = {
...contact,
phone: event.target.value
};
this.setState({ contact: newContact });
}
render() {
return (
<div>
<input type="text" onChange={this.changeFirstName} value={this.state.contact.firstName}/>
<input type="text" onChange={this.changeLastName} value={this.state.contact.lastName}/>
<input type="text" onChange={this.changePhone} value={this.state.contact.phone}/>
</div>
);
}
}
The "smart" way, ES2015+
Note that handleChangeFor is a curried function:
Calling it with a propertyName creates a callback function which, when called, updates [propertyName] of the
(new) contact object in the state.
class ContactEdit extends React.Component {
handleChangeFor = (propertyName) => (event) => {
const { contact } = this.state;
const newContact = {
...contact,
[propertyName]: event.target.value
};
this.setState({ contact: newContact });
}
render() {
return (
<div>
<input type="text" onChange={this.handleChangeFor('firstName')} value={this.state.contact.firstName}/>
<input type="text" onChange={this.handleChangeFor('lastName')} value={this.state.contact.lastName}/>
<input type="text" onChange={this.handleChangeFor('phone')} value={this.state.contact.lastName}/>
</div>
);
}
}

ES6 one liner approach
<input type="text"
value={this.state.username}
onChange={(e) => this.setState({ username: e.target.value })}
id="username"/>

The neatest approach
Here is an approach that I used in my simple application. This is the recommended approach in React and it is really neat and clean. It is very close to ArneHugo's answer and I thank hm too. The idea is a mix of that and react forms site.
We can use name attribute of each form input to get the specific propertyName and update the state based on that. This is my code in ES6 for the above example:
class ContactEdit extends React.Component {
handleChangeFor = (event) => {
const name = event.target.name;
const value = event.target.value;
const { contact } = this.state;
const newContact = {
...contact,
[name]: value
};
this.setState({ contact: newContact });
}
render() {
return (
<div>
<input type="text" name="firstName" onChange={this.handleChangeFor} />
<input type="text" name="lastName" onChange={this.handleChangeFor}/>
<input type="text" name="phone" onChange={this.handleChangeFor}/>
</div>
);
}
}
The differences:
We don't need to assign state as value attribute. No value is needed
The onChange method does not need to have any argument inside the function call as we use name attribute instead
We declare name and value of each input in the begening and use them to set the state properly in the code and we use rackets for name as it is an attribute.
We have less code here and vey smart way to get any kind input from the form because the name attribute will have a unique value for each input.
See a working example I have in CodPen for my experimental blog application in its early stage.

There are two ways to update the state of a nested object:
Use JSON.parse(JSON.stringify(object)) to create a copy of the object, then update the copy and pass it to setState.
Use the immutability helpers in react-addons, which is the recommended way.
You can see how it works in this JS Fiddle. The code is also below:
var Component = React.createClass({
getInitialState: function () {
return ({contact: {firstName: "first", lastName: "last", phone: "1244125"}});
},
handleChange: function (key,event) {
console.log(key,event.target.value);
//way 1
//var updatedContact = JSON.parse(JSON.stringify(this.state.contact));
//updatedContact[key] = event.target.value;
//way 2 (Recommended)
var updatedContact = React.addons.update(this.state.contact, {
[key] : {$set: event.target.value}
});
this.setState({contact: updatedContact});
},
render: function () {
return (
<div>
<input type="text" onChange={this.handleChange.bind(this,"firstName")} value={this.state.contact.firstName}/>
<input type="text" onChange={this.handleChange.bind(this,"lastName")} value={this.state.contact.lastName}/>
<input type="text" onChange={this.handleChange.bind(this,"phone")} value={this.state.contact.phone}/>
</div>
);
}
});
ReactDOM.render(
<Component />,
document.getElementById('container')
);

Here is generic one;
handleChange = (input) => (event) => {
this.setState({
...this.state,
[input]: event.target.value
});
}
And use like this;
<input handleChange ={this.handleChange("phone")} value={this.state.phone}/>

<input> elements often have a property called name.
We can access this name property from the event object that we receive from an event handler:
Write a generalized change handler
constructor () {
super();
this.state = {
name: '',
age: ''
};
this.handleChange = this.handleChange.bind(this);
}
handleChange (evt) {
this.setState({ [evt.target.name]: evt.target.value });
}
render () {
return (
<form>
<label>Name</label>
<input type="text" name="name" onChange={this.handleChange} />
<label>Age</label>
<input type="text" name="age" onChange={this.handleChange} />
</form>
);
}
source

updatePrevData=(event)=>{
let eventName=event.target.name;
this.setState({
...this.state,
prev_data:{
...this.state.prev_data,
[eventName]:event.target.value
}
})
console.log(this.state)
}

You can do it without duplicate code and easy way
handleChange=(e)=>{
this.setState({
[e.target.id]:e.target.value
})
}
<Form.Control type="text" defaultValue={this.props.allClients.name} id="clientName" onChange={this.handleChange}></Form.Control>
<Form.Control type="email" defaultValue={this.props.allClients.email} id="clientEmail" onChange={this.handleChange}></Form.Control>

handleChange(event){
this.setState({[event.target.name]:event.target.value});
this.setState({[event.target.name]:event.target.value});
}