We Keep Coding

Passing Index from mapped child component back up to Parent Component

Ill preface this question with I am fairly junior, so my code might not adhere to best practices. That said, I have been creating a "to-do" list with full CRUD functionality. So far, I have been able to successfully populate the task but have gotten stuck with updating the task. I am successfully updating the task when I hardcode the index but haven't been successful in dynamically updating, as I can't seem to pass the index back up to the parent component.
Within my Home component, I have the following.... Within, "handleSubmit" function, is where I am updating the list.
HOME
class Home extends Component {
constructor(props) {
super(props);
this.state = {
allTodos: {
todo: '',
description: '',
urgency: '',
date: new Date(),
},
showList: false,
arrayOfTodos: [],
showModal: false,
index: 0,
};
}
handleChangeTodo = (e) => {
this.setState({
allTodos: {
...this.state.allTodos,
todo: e.target.value,
},
});
};
handleChangeDescription = (e) => {
this.setState({
allTodos: {
...this.state.allTodos,
description: e.target.value,
},
});
};
handleChangeUrgency = (e) => {
this.setState({
allTodos: {
...this.state.allTodos,
urgency: e.target.value,
},
});
};
handleChangeDate = (date) => {
this.setState({
allTodos: {
...this.state.allTodos,
date: date,
},
});
};
handleSubmit = (e) => {
e.preventDefault();
this.setState((prevState) => ({
arrayOfTodos: [...prevState.arrayOfTodos, prevState.allTodos],
allTodos: { todo: '', description: '', urgency: '', date: new Date() },
}));
this.setState({ showList: true });
if (this.state.showModal) {
this.state.arrayOfTodos.splice(0, 1);
this.setState({ showModal: false });
}
};
handleShowModal = () => {
this.setState({ showModal: true });
};
render() {
console.log(this.state.arrayOfTodos);
return (
<div>
<header> Task Buddy</header>
<div>
<form>
<label>
To-Do:
<input
type='text'
name='todo'
value={this.state.allTodos.todo}
onChange={this.handleChangeTodo}
/>
</label>
<label>
Description:
<input
type='text'
name='description'
onChange={this.handleChangeDescription}
value={this.state.allTodos.description}
/>
</label>
<label>
Urgency:
<input
type='text'
name='urgency'
onChange={this.handleChangeUrgency}
value={this.state.allTodos.urgency}
/>
</label>
<label>
Date:
<Calendar
// value={this.state.date}
onChange={this.handleChangeDate}
value={this.state.allTodos.date}
/>
</label>
<button onClick={this.handleSubmit}> Submit</button>
</form>
{this.state.showList && (
<div>
<Todos
index={this.state.index}
todo={this.state.arrayOfTodos}
showModal={this.state.showModal}
handleShowModal={this.handleShowModal}
/>
</div>
)}
{this.state.showModal && (
<div>
<Modal
todo={this.state.arrayOfTodos}
handleChangeTodo={this.handleChangeTodo}
handleChangeDescription={this.handleChangeDescription}
handleChangeUrgency={this.handleChangeUrgency}
handleChangeDate={this.handleChangeDate}
handleSubmit={this.handleSubmit}
/>
</div>
)}
</div>
</div>
);
}
}
export default Home;
TODOS
const Todos = (props) => {
console.log(props.index);
return (
<div>
{props.todo.map((x, index) => {
return (
<div>
<li key={index}>
{index}
{x.todo} {x.description} {x.urgency} {x.date.toString()}{' '}
<button onClick={props.handleShowModal}>Update</button>
<button> Delete</button>
</li>
</div>
);
})}
</div>
);
};
export default Todos;
MODAL
class Modal extends Component {
render(props) {
return (
<div>
<form>
<label>
To-Do:
<input
type='text'
name='todo'
value={this.props.todo.todo}
onChange={this.props.handleChangeTodo}
placeholder={this.props.todo.todo}
/>
</label>
<label>
Description:
<input
type='text'
name='description'
onChange={this.props.handleChangeDescription}
value={this.props.todo.description}
/>
</label>
<label>
Urgency:
<input
type='text'
name='urgency'
onChange={this.props.handleChangeUrgency}
value={this.props.todo.urgency}
/>
</label>
<label>
Date:
<Calendar
// value={this.state.date}
onChange={this.props.handleChangeDate}
value={this.props.todo.date}
/>
</label>
<button onClick={this.props.handleSubmit}> Submit</button>
</form>
</div>
);
}
}
export default Modal;

I'll give somewhat abstract answer with general practices that I often encounter and use.
Basically, there is one proper way to pass data from child component to parent component - via functions that passed from parent and called in child. If said data accessible in parent beforehand (e.g. during render) you can construct function with closure in such way that each component will call their own version of function with data already included. It will look somewhat like this:
render() {
return (
<>
{collection.map((item, index) => (
<Component
onEvent={(params) => {
/* You can use index and all other data accessible in parent together with params that were passed from component */
}}
/>
))}
</>
);
}
Another way is to construct handler in such way that you will pass in it all data that you need to pass. So, for example, if you tracking "change" event from input and can't rely on input name or id, you can pass additional data in your handler along with event like this:
// Parent.js
class Parent {
handleInputChange = (event, index) => {
/* do something with event index passed from child */
};
render() {
return (
<>
{collection.map((item, index) => (
<ComponentWithInput
key={index}
index={index}
onChange={this.handleChange}
/>
))}
</>
);
}
}
// Child.js
function ComponentWithInput(props) {
return <input onChange={(event) => props.onChange(event, props.index)} />;
}
Generally speaking, functions that you pass to child component is a way of communication in up direction, so you design these function not based solely on DOM events, but on data that you need to pass up. Sometimes you don't need DOM events at all, apart from the fact that they happened.

Updating React state with Hooks and tags

I'm having a syntax doubt on how to update React state using hooks in 2 situations.
1) I have a state called company and a form that fills it up. In contact section, there are two inputs referring to the company employee (name and telephone number). But if the company has more than one employee to be contacted, there is an "Add More Contact" button, which must duplicate the same inputs (of course, aiming to a second contact). How can I do that? I mean, to generate another index in the array "contacts" inside the state, increment the totalOfContacts inside the object that has that array and create the input tags so user can type the second contact's data?
2) When I type any inputs, the code triggers the handleChange function. The "name" and "city" already update the state because they are simple states. But how can I update the contact name and his telephone number, since they are part of an index of an array inside the state?
The code below is already working and my 2 questions are exactly the two commented lines (lines 20 and 29).
The "Save" button simply console.log the results so we can monitor them.
Thanks for now.
import React, { useState, useEffect } from "react";
export default () => {
const [company, setCompany] = useState({
name: "", city: "",
contact: {
totalOfContact: 1,
contacts: [
{id: 0, contactName: "", telephoneNumber: ""}
]
}
})
useEffect(() => {
console.log("teste");
})
const handleChange = item => e => {
if (item === "contactName" || "telephone") {
// How can I set company.contact.contacts[<current_index>].contactName/telephoneNumber with the data typed?
} else {
setCompany({ ...company, [item]: e.target.value })
}
}
const handleClick = (e) => {
e.preventDefault();
if (e.target.value === "add") {
// How can I set company.contact.totalOfContact to 2 and create one more set of inputs tags for a second contact?
} else {
console.log(`The data of the company is: ${company}`);
}
}
return (
<div>
<form>
<h3>General Section</h3>
Name: <input type="text" onChange = {handleChange("name")} value = {company.name} />
<br />
City: <input type="text" onChange = {handleChange("city")} value = {company.city} />
<br />
<hr />
<h3>Contacts Section:</h3>
Name: <input type="text" onChange = {handleChange("contactName")} value = {company.contact.contacts[0].name} />
Telephone Numer: <input type="text" onChange = {handleChange("telephone")} value = {company.contact.contacts[0].telephoneNumber} />
<br />
<br />
<button value = "add" onClick = {(e) => handleClick(e)} >Add More Contact</button>
<br />
<br />
<hr />
<button value = "save" onClick = {(e) => handleClick(e)} >Save</button>
</form>
</div>
)
}

To update the state value, you can use functional setState,
const handleChange = item => e => {
//Take the value in a variable for future use
const value = e.target.value;
if (item === "contactName" || "telephone") {
setCompany(prevState => ({
...prevState,
contact: {...prevState.contact, contacts: prevState.contact.contacts.map(c => ({...c, [item]: value}))}
}))
} else {
setCompany({ ...company, [item]: e.target.value })
}
}
To add new set of input on the click of button you can do this,
const handleClick = (e) => {
e.preventDefault();
//This is new set of input to be added
const newSetOfInput = {id: company.contact.contacts.length, contactName: "", telephoneNumber: ""}
if (e.target.value === "add") {
// How can I set company.contact.totalOfContact to 2 and create one more set of inputs tags for a second contact?
setCompany(prevState => ({
...prevState,
contact: {...prevState.contact, contacts: prevState.contact.contacts.concat(newSetOfInput), totalOfContact: prevState.contact.contacts.length + 1}
}))
} else {
console.log(`The data of the company is: ${company}`);
}
}
Finally you need to iterate over your contacts array like,
{company.contact.contacts && company.contact.contacts.length > 0 && company.contact.contacts.map(contact => (
<div key={contact.id}>
Name: <input type="text" onChange = {handleChange("contactName")} value = {contact.contactName} />
<br/>
Telephone Numer: <input type="text" onChange = {handleChange("telephoneNumber")} value = {contact.telephoneNumber} />
</div>
))}
Demo
Note: You should use block elements like div instead of breaking the line using <br/>

To answer your question let us scope down this problem to a much simpler problem, which is how to handle array of contacts.
You just need know the following things:
Map function
How to update array without mutating the original array
I'll use TypeScript so you can understand better.
const [state, setState] = React.useState<{
contacts: {name: string}[]
}>({contacts: []})
return (
<div>
{state.contacts.map((contact, index) => {
return (
<div>
Name:
<input value={contact.name} onChange={event => {
setState({
...state,
contacts: state.contacts.map((contact$, index$) =>
index === index$
? {...contact$, name: event.target.value}
: {...contact$}
)
})
}}/>
</div>
)
}}
</div>
)
Also, this kind of problem is fairly common in React, so understand and memorize this pattern will help you a lot.

You can do something like this.
import React, { useState, useEffect } from "react";
import ReactDOM from "react-dom";
const App = () => {
const [company, setCompany] = useState({
name: "",
city: "",
contact: {
totalOfContact: 1,
contacts: [{id: 0, contactName: "", telephoneNumber: ""}]
}
});
console.log(company);
useEffect(() => {
console.log("teste");
}, []);
const handleChange = (item, e,index) => {
if (item === "contactName" || item === "telephoneNumber") {
const contactsNew = [...company.contact.contacts];
contactsNew[index] = { ...contactsNew[index], [item]: e.target.value };
setCompany({
...company,
contact: { ...company.contact, contacts: contactsNew }
});
// How can I set company.contact.contacts[<current_index>].contactName/telephoneNumber with the data typed?
} else {
setCompany({ ...company, [item]: e.target.value });
}
};
const handleClick = e => {
e.preventDefault();
if (e.target.value === "add") {
const contactNew = {...company.contact};
contactNew.totalOfContact = contactNew.totalOfContact + 1;
contactNew.contacts.push({id:contactNew.totalOfContact -1, contactName: "", telephoneNumber: ""});
setCompany({...company, contact: {...contactNew}});
// How can I set company.contact.totalOfContact to 2 and create one more set of inputs tags for a second contact?
} else {
alert("Push company to somewhere to persist");
console.log(`The data of the company is: ${company}`);
}
};
return (
<div>
<form>
<h3>General Section</h3>
Name:{" "}
<input
type="text"
onChange={(e) => handleChange("name", e)}
value={company.name}
/>
<br />
City:{" "}
<input
type="text"
onChange={(e) => handleChange("city", e)}
value={company.city}
/>
<br />
<hr />
<h3>Contacts Section:</h3>
{company.contact.contacts.map((eachContact, index) => {
return <React.Fragment>
Name:{" "}
<input
type="text"
onChange={(e) => handleChange("contactName",e, index)}
value={eachContact.name}
/>
Telephone Numer:{" "}
<input
type="text"
onChange={(e) => handleChange("telephoneNumber",e, index)}
value={eachContact.telephoneNumber}
/>
<br />
</React.Fragment>
})}
<br />
<button value="add" onClick={e => handleClick(e)}>
Add More Contact
</button>
<br />
<br />
<hr />
<button value="save" onClick={e => handleClick(e)}>
Save
</button>
</form>
</div>
);
};
const rootElement = document.getElementById("root");
ReactDOM.render(<App />, rootElement);
Your state structure looks like an ideal candidate for useReducer hook. I would suggest you try that instead of useState. Your code should look muck readable that way, I suppose. https://reactjs.org/docs/hooks-reference.html#usereducer

Why changing state (props based) in child component can effect the props?

You can see demo here. Try to click "Edit" button and change the value of input field.
In the parent component, it pass an array of objects to its child. Inside the child component, one of objects can be passed into its state, named editedTodo. But, strangely, the prop is changed when editedTodo is changed.
This is not what I want. Anyone can help me solve this?
Here is the todo Component:
import React from "react";
export default class extends React.Component {
state = {
editedTodo: null
};
toggleEditTodo = (todo = null) => {
this.setState({ editedTodo: todo });
};
onChangeTodoText = text => {
this.setState(prevState => ({
editedTodo: Object.assign(prevState.editedTodo, { text })
}));
};
submitTodoForm = e => {
e.preventDefault();
this.props.saveEditedTodo(this.state.editedTodo);
this.setState({
editedTodo: null
});
};
render() {
const { editedTodo } = this.state;
const { todos } = this.props;
return (
<ul>
<li>{JSON.stringify(todos)}</li>
{todos.map(todo => (
<li key={todo.id}>
{todo === editedTodo ? (
<form onSubmit={this.submitTodoForm}>
<input
autoFocus
value={editedTodo.text}
onChange={e => this.onChangeTodoText(e.target.value)}
/>
<button type="submit">Save</button>
<button type="button" onClick={this.toggleEditTodo}>
Cancel
</button>
</form>
) : (
<span>
{todo.text}
<button onClick={() => this.toggleEditTodo(todo)}>Edit</button>
</span>
)}
</li>
))}
</ul>
);
}
}

https://codesandbox.io/s/3q1k4m3vm5
Here is the working version.
The problem was with this.setState({ editedTodo: todo }). You are assigning the same copy of todo from the props to the state. So it is referencing the same item. Make sure you are never mutating your props directly, it is an anti-pattern.

Printing list in <ul>

I want to print a new <ul> list of <li> movies.
I don't see any list nor elements.
I also get a warning:
index.js:2178 Warning: A component is changing an uncontrolled input of type text to be controlled. Input elements should not switch from uncontrolled to controlled (or vice versa). Decide between using a controlled or uncontrolled input element for the lifetime of the component. More info: https://reactjs.org/docs/forms.html#controlled-components
in input (at index.js:54)
in label (at index.js:52)
in form (at index.js:51)
in div (at index.js:50)
in Movie (at index.js:70)
This is my code:
class Movie extends React.Component {
constructor(props) {
super(props);
this.state = {value: '',
list: [],
checked: true
};
this.handleChange = this.handleChange.bind(this);
this.handleSubmit = this.handleSubmit.bind(this);
this.addMovie = this.addMovie.bind(this);
this.listMovies = this.listMovies.bind(this);
}
handleChange(event) {
const target = event.target;
const value = target.type === 'checkbox' ? target.checked : target.value;
const name = target.name;
this.setState({
[name]: value
});
}
handleSubmit(event) {
event.preventDefault();
this.addMovie();
}
addMovie(value){
this.setState({ list: [...this.state.list, value] });
console.log(...this.state.list);
}
listMovies(){
return(
<ul>
{this.state.list.map((item) => <li key={this.state.value}>{this.state.value}</li>)}
</ul>
);
}
render() {
return (
<div>
<form onSubmit={this.handleSubmit}>
<label>
Movie name:
<input name="movieName" type="text" value={this.state.movieName} onChange={this.handleChange} />
Favorite?
<input name="favorite" type="checkbox" checked={this.state.favorite} onChange={this.handleChange} />
</label>
<input type="submit" value="Submit" />
</form>
<button onClick={this.listMovies}>
List Movies
</button>
</div>
);
}
}
ReactDOM.render(
<Movie />,
document.getElementById('root')
);
I would really want to print only my Favorites movies

I'm guessing you want a simple movies list with favorites. Not the best one but working code:
import React from 'react';
import { render } from 'react-dom';
class App extends React.Component {
state = {
favorite: false,
movieName: "",
movies: [],
filter: true,
};
handleChange = (event) =>
event.target.name === "favorite"
? this.setState({ [event.target.name]: event.target.checked })
: this.setState( { [ event.target.name]: event.target.value } );
handleSubmit = ( event ) => {
event.preventDefault();
this.setState({
movies: [...this.state.movies, {name: this.state.movieName, favorite: this.state.favorite }]
});
}
listFavoriteMovies = () => (
<ul>
{this.state.movies
.filter( movie => movie.favorite )
.map( movie => <li>{movie.name}</li>)}
</ul>
);
listAllMovies = () => (
<ul>
{this.state.movies
.map(movie => <li>{movie.name}</li>)}
</ul>
);
changeFilter = () =>
this.setState( prevState => ( {
filter: !prevState.filter,
}))
render() {
return (
<div>
<form onSubmit={this.handleSubmit}>
<label>
Movie name:
<input name="movieName" type="text" onChange={this.handleChange} />
Favorite?
<input name="favorite" type="checkbox" onChange={this.handleChange} />
</label>
<input type="submit" value="Submit" />
</form>
<p>Showing only favorite movies.</p>
<ul>
{
this.state.filter
? this.listFavoriteMovies()
: this.listAllMovies()
}
</ul>
<button onClick={this.changeFilter}>Click toggle for all/favorites.</button>
</div>
);
}
}
render(<App />, document.getElementById('root'));

if you initially pass undefined or null as the value prop, the
component starts life as an "uncontrolled" component. Once you
interact with the component, we set a value and react changes it to a
"controlled" component, and issues the warning.
In your code initialise movieName in your state to get rid of warning.
For more information check here

React Todo Checkbox Styles all listed items at once

I'm trying to create a todo-list with React. I am able to display the list in the display area and also able to remove the items. But when I click on one checkbox, all the checkboxes are selected and the class is applied to all the list items. I'm not sure what is it that I am doing wrong.
I tried to use the same logic as I did with the deleted item(that's using the filter), but it doesn't work. I looked other cases here but they are mostly about how to do it with jQuery.
Here is the working example of my problem.
This is the List class
class List extends Component {
state={
check: false,
strike: 'none'
}
onCheck(item){
this.setState({check: !this.state.check})
if (this.state.strike === 'none'){
this.setState({strike: 'line-through'})
} else {
this.setState({strike: 'none'})
}
}
render() {
const strike = {
textDecoration: this.state.strike,
}
return (
<ul className='list-style'>
{ this.props.items.map((item, index) =>
<li key={index}>
<div className="outer-div">
<div className="item-checkbox">
<input type="checkbox" checked={this.state.check}
onChange={() => this.onCheck(item)} />
</div>
<div className="item-text">
<span style= {strike}> {item} </span>
</div>
<div className="item-remove-div">
<button className="item-remove" onClick={() => this.props.onDeleteList(index)}>
Remove
</button>
</div>
</div>
<br />
</li>
)}
</ul>
)}
}
export default List;
And this is the Main Class:
class Main extends Component {
state = {
items: [],
term : "",
}
onChange(event){
this.setState({ term: event });
}
onDelete= (item) =>{
// this.setState ({
// items: this.state.items.filter((i) => i.index !== item.index)
// })
this.state.items.splice(item, 1);
this.setState({items: this.state.items});
}
onSubmit= (event) => {
event.preventDefault();
if (this.state.term.length > 0){
this.setState({
term: '',
items: [...this.state.items, this.state.term]
});
}
}
render() {
return (
<div className="center">
<h1 className="header" > TODO-LIST </h1>
<div className='mainCenter'>
<form className="App" onSubmit={this.onSubmit}>
<input placeholder="add task" value={this.state.term} onChange={(e) => this.onChange(e.target.value)}
className="inputField"/>
<button>Add to the List</button>
</form>
<List items={this.state.items} onDeleteList={this.onDelete}/>
<div className="footer-outer">
<span className="footer"> Number of completed items in an array: {this.state.items.length} </span>
</div>
</div>
</div>
);
}
}

I edited your SlackBlitz. Now you can properly add new todos, check individuals tasks (toggle checked on todo click) and see correct checked counter in the footer.
Check todo-list-react demo.
import React, { Component } from 'react';
import TodoList from './List';
import './style.css';
class Main extends Component {
constructor() {
super();
this.state = {
items: [],
term: ''
};
}
handleChange = event => {
this.setState({ term: event.target.value });
}
handleItemClick = ({ value, checked }) => {
this.setState({
items: this.state.items.map(item => item.value === value ? { value, checked: !checked } : item)
});
}
onSubmit = event => {
event.preventDefault();
if (this.state.term.length > 0) {
this.setState({
term: '',
items: [...this.state.items, { value: this.state.term, checked: false }]
});
}
}
handleDelete = index => {
console.info('todo: remove todo at index', index);
// deletion logic... keep in mind that using index as key properties on jsx could breaks the correct functioning of this component.
}
render() {
return (
<div className="center">
<h1 className="header" > TODO-LIST </h1>
<div className='mainCenter'>
<form className="App" onSubmit={this.onSubmit}>
<input placeholder="add task" value={this.state.term} onChange={this.handleChange}
className="inputField"/>
<button>Add to the List</button>
</form>
<TodoList
onTodoClick={this.handleItemClick}
onDelete={this.handleDelete}
todos={this.state.items}
/>
<div className="footer-outer">
<span className="footer">
Number of completed items in an array:
{this.state.items.filter(item => item.checked).length}
</span>
</div>
</div>
</div>
);
}
}
export default Main
import React, { Component } from 'react';
import './style.css';
class List extends Component {
render() {
const { todos, onTodoClick, onDelete } = this.props;
return (
<ul className='list-style'>
{
todos.map((item, index) =>
<li key={index}>
<div className="outer-div">
<div className="item-checkbox">
<input type="checkbox" checked={item.checked}
onChange={() => onTodoClick(item)} />
</div>
<div className="item-text">
<span style={checkboxStyle(item.checked)}>{item.value}</span>
</div>
<div className="item-remove-div">
<button className="item-remove"
onClick={() => onDelete(index)}>
Remove
</button>
</div>
</div>
<br />
</li>
)}
</ul>
)}
}
function checkboxStyle(checked) {
return {
textDecoration: checked? 'line-through' : 'none',
};
}
export default List;
In addition to this answer, I recommend you to consider to add an unique key property to each jsx-element differen from the array index. Current implementation has no problem, but once you start deleting todo items probably display wrong data.
Read List and Keys from React docs and this article on Medium which covers possible error when using indixes as keys.

The reason that all your list items are being 'striked' is because you have only one state reserved for all the items in the list. You need to have the checked or strike state for each item in the list. However, as I view your comments, I realize that you already know that.
You have several other inconsistencies in the code:
onDelete= (item) =>{
this.state.items.splice(item, 1);
this.setState({items: this.state.items});
}
Making direct changes to the state like that might cause unwanted errors and unusual behavior. A better way to do it is to:
onDelete = (item) => {
const items = this.state.items.slice();
items.splice(item, 1);
this.setState({
items: items,
});
}
For more info refer to this article:
https://medium.com/pro-react/a-brief-talk-about-immutability-and-react-s-helpers-70919ab8ae7c