We Keep Coding

Passing onChange event from mapped child to parent's state returns 'undefined' error

Hello [from react beginner].
Trying to pass child's input value to parent state.
So, App has an array:
export default class App extends React.Component {
state = {
data: [
{id: 1, name: 'john'},
{id: 2, name: 'doe'},
]
}
render() {
return (
<List data={this.state.data}/>
)
}
}
Then List takes prop.data as state.data and returns children in map:
class List extends React.Component {
constructor(props) {
super(props);
this.state = {
data: this.props.data
};
this.parentChange = this.parentChange.bind(this);
}
renderList() {
const data = this.state.data;
let list = null;
if (data.length) {
list = data.map(function(item, index){
return (<Item key={item.id} data={item} onChange={(e, index) => this.parentChange(e, index)} />)
});
} else {
list = <p>nothing here</p>
}
return list;
}
parentChange(value, index) {
// pls give me anything
console.log('--- value: ', value);
console.log('--- index: ', index);
}
render() {
return (
<div>{this.renderList()}</div>
)
}
}
And Item child:
class Item extends React.Component {
render() {
const {id, name} = this.props.data;
return (
<div>
<input id={id} value={name} onChange={(e) => this.props.onChange(e, id)} />
</div>
)
}
}
But if I change any input's value there is an error as result
Cannot read property 'parentChange' of undefined
Thanks for any help (code, links etc)

You are declaring a function with function keyword:
if (data.length) {
list = data.map(function(item, index){
return (<Item key={item.id} data={item} onChange={(e, index) =>
this.parentChange(e, index)} />)
});
}
Declaring a function with the function keyword will create another context inside itself, so your this (context) will no longer be the class context.
The IDE might not warn you but when it runs, JS create another context inside your function result in an undefined error.
So it will need to change to:
if (data.length) {
list = data.map((item, index) => {
return (<Item key={item.id} data={item} onChange={(e, index) =>
this.parentChange(e, index)} />)
});
}

Set input to a controller input using button onclick method in React JS

I find myself struggling to change the form input value from the button onClick handler. My problem is escalated by the fact that I have the line items on a form and things become even more complex that way. I tried to bring in a ref to set value,,, the value is displayed but at the form state after submission it remains empty which means the value is not being set. Below are all my code files. May someone kindly help me on where I may be missing the point.
class VehicleTemplate extends React.Component {
constructor(props){
super(props);
this.ws = new WebSocket('ws://localhost:8000/ws/weightData/');
this.socketRef = null;
this.state = {
data: 0,
name: '',
model: '',
plate_number: '',
type: 'truck',
wagons: [{ index: uuid(), label: '', type: 'once', weight: '' }],
total: 0,
};
this.onSubmit = this.onSubmit.bind(this);
this.handleChange= this.handleChange.bind(this);
this.handleChangeTable = this.handleChangeTable.bind(this);
this.addNewRow = this.addNewRow.bind(this);
this.deleteRow = this.deleteRow.bind(this);
this.handleLineItemChange = this.handleLineItemChange.bind(this);
}
componentDidMount() {
this.ws.onopen = () => {
// on connecting, do nothing but log it to the console
console.log('connected')
}
this.ws.onmessage = evt => {
// listen to data sent from the websocket server
// const message = JSON.parse(evt.data)
const {data} = this.state;
this.setState({data: evt.data})
// this.setState({this.state.lines.weight: data})
}
this.ws.onclose = () => {
console.log('disconnected')
// automatically try to reconnect on connection loss
}
};
onSubmit = (e) => {
e.preventDefault();
const {
name,
model,
plate_number,
type,
wagons,
} = this.state;
const vehicle = {
name,
model,
plate_number,
type,
wagons,
};
this.props.addVehicle(vehicle, this.props.token);
console.log(vehicle);
this.setState({
name: '',
model: '',
plate_number: '',
wagons: [],
});
};
handleLineItemChange = (elementIndex) => (event) => {
let wagons = this.state.wagons.map((item, i) => {
if (elementIndex !== i) return item
return {...item, [event.target.name]: event.target.value}
})
this.setState({wagons})
}
handleChange = name => event => {
this.setState({
[name]: event.target.value,
});
};
handleChangeTable = (name, id) => event => {
this.updateItem(id, { [name]: event.target.value });
};
addNewRow = (event) => {
this.setState({
wagons: this.state.wagons.concat(
[{index: uuid(), label: '', type: 'once', weight: '' }]
)
})
}
deleteRow = (index) => (event) => {
this.setState({
wagons: this.state.wagons.filter((item, i) => {
return index !== i
})
})
}
handleReorderLineItems = (newLineItems) => {
this.setState({
wagons: newLineItems,
})
}
clickOnDelete(record) {
this.setState({
wagons: this.state.lines.filter(r => r !== record)
});
}
render() {
const { classes } = this.props;
const {
data,
name,
model,
plate_number,
wagons,
} = this.state;
return (
<InformationTechnologyLayout>
<PapperBlock title="ADD VEHICLE" icon="ios-document-outline" desc="VEHICLE">
<Form>
<div style={{ clear: 'both' }} />
<h1>WEIGHT: {data}KG</h1>
<Grid container>
<Grid item xs={6}>
<Controls.Input
name="name"
label="Name"
value={name}
onChange={this.handleChange('name')}
/>
<Controls.Input
name="model"
label="MODEL"
value={model}
onChange={this.handleChange('model')}
/>
</Grid>
<Grid item xs={6}>
<Controls.Input
name="plate_number"
label="PLATE NUMBER"
value={plate_number}
onChange={this.handleChange('plate_number')}
/>
</Grid>
</Grid>
<Extensions
items={wagons}
addHandler={this.addNewRow}
changeHandler={this.handleLineItemChange}
focusHandler={this.handleFocusSelect}
deleteHandler={this.deleteRow}
reorderHandler={this.handleReorderLineItems}
data ={data}
/>
<div className='valueTable'>
<div className='row'>
<div className='label'>Subtotal</div>
<div className='value'>{this.calcLineItemsTotal()}KG</div>
</div>
<div className='row'>
<div className='label'>Total Due</div>
<div className='value'>{this.calcGrandTotal()}KG</div>
</div>
</div>
<Button variant="contained" onClick={this.onSubmit}>SUBMIT</Button>
</Form>
</PapperBlock>
</InformationTechnologyLayout>
);
}
}
On top is the main form component which has got Vehicle exetnsions and I am getting my weight from a websocket connection streaming scale outputs.
class Extensions extends Component {
handleDragEnd = (result) => {
if (!result.destination) return
// helper function to reorder result (src: react-beautiful-dnd docs)
const reorder = (list, startIndex, endIndex) => {
const result = Array.from(list)
const [removed] = result.splice(startIndex, 1)
result.splice(endIndex, 0, removed)
return result
}
// perform reorder
const lineItems = reorder(
this.props.items,
result.source.index,
result.destination.index
)
// call parent handler with new state representation
this.props.reorderHandler(lineItems)
}
render = () => {
const {
items,
addHandler,
changeHandler,
focusHandler,
deleteHandler,
reorderHandler,
products,
data,
readOnly,
} = this.props
return (
<form>
<div className='lineItems'>
<div className='gridTable'>
<DragDropContext onDragEnd={this.handleDragEnd}>
<Droppable droppableId="droppable">
{(provided, snapshot) => (
<div
ref={provided.innerRef}
className= 'listDraggingOver'
>
{this.props.items.map((item, i) => (
<Draggable key={item.index} draggableId={item.index} index={i}>
{(provided, snapshot) => (
<div
ref={provided.innerRef}
{...provided.draggableProps}
{...provided.dragHandleProps}
style={provided.draggableProps.style}
className='listItemDragging'
>
<Extension
addHandler={addHandler}
changeHandler={changeHandler}
focusHandler={focusHandler}
deleteHandler={deleteHandler}
reorderHandler={reorderHandler}
data={data}
style={{color: 'red'}}
key={i + item.index}
index={i}
name={item.index}
label={item.label}
weight={item.weight}
/>
</div>
)}
</Draggable>
))}
{provided.placeholder}
</div>
)}
</Droppable>
</DragDropContext>
</div>
<div className='addItem'>
<button type="button" onClick={addHandler}><AddIcon size="1.25em" className='addIcon' /> Add Item</button>
</div>
</div>
</form>
)
}
}
This are the extensions and the last file is where I would like to capture weight from
class LineItem extends Component {
constructor(props){
super(props);
this.ref = React.createRef();
this.state = {
buttonState: false,
};
}
requestWeight = () => {
const { weight } = this.props;
const {buttonState} =this.state;
this.ref.current.value = this.props.data;
this.setState({
buttonState: true
})
};
render = () => {
const { index, label, weight } = this.props;
const {buttonState} = this.state;
return (
<div className='lineItem'>
<div>{index + 1}</div>
<Controls.Input
name="label"
label="LABEL"
value={label}
onChange={this.props.changeHandler(index)}
/>
<input
className='currency'
type='number'
readOnly={true}
ref={this.ref}
name='weight'
onChange={this.props.changeHandler(index)}
/>
<div>
<button type="button"
className='requestItems'
onClick={this.requestWeight}
disabled={buttonState}
>REQUEST WEIGHT</button>
</div>
<div>
<button type="button"
className='deleteItem'
onClick={this.props.deleteHandler(index)}
><DeleteIcon size="1.25em" /></button>
</div>
</div>
)
}
}
export default LineItem
If I add the value and put weight on the input then the ref stops working. I assume I might be missing something between my handleChange function and the requestWeight function but I really dont know what exaclty

using checkboxes to change state and sort list

I have a list like this:
<div className="doubleCol">
{this.state.symptoms.map(item => (
<ListItem key={item.ObjectID}>
<input type="checkbox" className="sympSelect" />
{item.name}
</ListItem>
))}
</div>
All the items rendered have checkbox and I want it to filter a different list elsewhere on the page based on which boxes are checked. To do that I need the checkboxes to change the state and pass the new state to a method which is supposed to filter and display only those items on the second list with id's associated to items on the first list.
From what I have read it shouldn't matter for this purpose if the checkboxes are controlled or uncontrolled.
class Home extends React.Component {
state = {
conditions: [],
symptoms: [],
selectedSymptom: []
}
componentDidMount() {
this.getConditionsMethod();
this.getSymptomsMethod();
}
getConditionsMethod = () => {
API.getConditions()
.then(data => {
console.log(data);
data.data.sort((a, b) => a.name.localeCompare(b.name))
this.setState({
conditions: data.data
})
})
.catch(err => console.log(err))
};
filterConditionsMethod = () => {
API.getConditions()
.then(data => {
console.log(data);
data.data.sort((a, b) => a.name.localeCompare(b.name));
this.setState({
selectedSymptom: data.data
})
})
.catch(err => console.log(err))
};
But I am kind of stuck on how to structure the onChange for when the box is checked and how to make that implement the filter.

Here is you solution you can add onChange event for checkbox and filter your records as selectedSymptoms and symptoms. Please check code is
import React, { Component } from "react";
class Home extends Component {
constructor(props) {
super(props);
this.state = {
conditions: [],
symptoms: [
{ ObjectID: 1, name: "xyz" },
{ ObjectID: 2, name: "pqr" }
],
selectedSymptom: [],
checked: ""
};
}
updateCheckBox = (event, item) => {
if (event.target.checked) {
let selectedList = this.state.selectedSymptom;
selectedList.push(item);
this.setState({
...this.state,
checked: this.state.checked == "checked" ? "" : "checked",
selectedSymptom: selectedList
});
} else {
const symptomss = this.state.selectedSymptom.filter(element => {
if (element.ObjectID != data.ObjectID) {
return item;
}
});
this.setState({
...this.state,
checked: "",
selectedSymptom: symptomss
});
}
};
render() {
return (
<div className="doubleCol">
{this.state.symptoms.map(item => (
<ListItem key={item.ObjectID}>
<input
type="checkbox"
className="sympSelect"
onChange={this.updateCheckBox(e, item)}
id="symptoms_id"
defaultChecked={this.state.checked}
/>
{item.name}
</ListItem>
))}
</div>
);
}
}
export default Home;

ReactJS: Adding multiple input fields of different types on click

I've created a React app for a school project that can add multiple types of input fields to a view by clicking a button (sort of like Wordpress Gutenberg).
Currently, I can add one of each type of item onto the view. However, if I click the button again, it erases the current text that was added. I'd like the ability to click the button to add as many fields as I'd like on click.
Also, the items are only added into the view in the order they were created meaning, even if I choose photo first and I click headline after, it (headline) will appear at the top of the list above the initial item.
I've had a look at these solutions (which were pretty good) but they didn't provide what I need.
Dynamically adding Input form field issue reactjs
and "update delete list elements using unique key": https://www.youtube.com/watch?v=tJYBMSuOX3s
which was closer to what I needed to do.
Apologies in advance for the length of the code,(there are two other related components for text input and an editform). I'm sure there is a much more simple way to do this. I haven't been able to find an npm package or solution to this specific problem online and am open to a simpler solution.
Edit.jsx
export default class Edit extends React.Component {
state = {
texts: {
hl: '',
shl: '',
txt: '',
photo: []
},
coms: {
hl: false,
shl: false,
txt: false,
photo: null
},
labels: {
// Replace with icons
hl: 'Headline',
shl: 'Sub',
txt: 'Text Area',
photo: 'Photo'
},
selectedItem: '',
}
componentDidMount() {
const saveData = localStorage.getItem('saveData') === 'true';
const user = saveData ? localStorage.getItem('user') : '';
this.setState({ user, saveData });
}
createPage = async () => {
await this.props.postPage(this.state.texts)
}
// add options
addOptions = (item) => {
const { coms } = this.state
coms[item] = !coms[item]
this.setState({ coms: coms })
}
// ADD TEXT
addTxt = () => {
this.setState({ texts: [...this.state.texts, ""] })
}
enableAllButtons = () => {
this.setState({ selectedItem: '' })
}
handleChange = (e, index) => {
this.state.texts[index] = e.target.value
//set the changed state.
this.setState({ texts: this.state.texts })
}
setDisable = (selectedItem) => {
this.setState({ selectedItem })
}
handleRemove = () => {
// this.state.texts.splice(index, 1)
this.setState({ texts: this.state.texts })
}
handleSubmit = (e) => {
console.log(this.state, 'all text')
}
handleChange = (e, item) => {
let { texts } = this.state
texts[item] = e.target.value
//set the changed state.
this.setState({ texts })
console.log(texts)
}
render() {
const { coms, labels, selectedItem, texts } = this.state
let buttons = Object.keys(coms)
let showItems = Object.keys(coms).filter(key => coms[key] === true)
return (
<div>
<InnerHeader />
{/* Make a route for edit here */}
<Route path='/edit/form' render={() => (
<EditForm
texts={texts}
coms={coms}
labels={labels}
addOptions={this.addOptions}
setDisable={this.setDisable}
selectedItem={selectedItem}
showItems={showItems}
handleChange={this.handleChange}
enableAllButtons={this.enableAllButtons}
/>
)} />
{/* Make route for preview */}
<Route path='/edit/preview' render={(props) => (
<Preview
{...props}
createPage={this.createPage}
/>
)}
/>
</div>
)
}
}
AddText.jsx:
export default class AddText extends Component {
state = {
}
// ADD TEXT
addTxt(item) {
const {
addOptions } = this.props
addOptions(item)
}
render() {
const { coms, labels } = this.props
const { selectedItem } = this.props
let buttons = Object.keys(coms)
console.log('here', selectedItem)
return (
<div>
<Card>
<Card.Body>
{
buttons.map((item, index) => <button
value={(selectedItem === "") ? false : (selectedItem === item) ? false : true} key={index} onClick={() => this.addTxt(item)}>
{labels[item]}
</button>
)
}
</Card.Body>
</Card>
</div>
)
}
}
EditForm.jsx
export default function EditForm(props) {
return (
<div>
<div className='some-page-wrapper-sm'>
<div className="dash-card-sm">
<button><Link to={{
pathname: '/edit/preview',
item: props.texts
}}>preview</Link></button>
<br />
<br />
<AddText
coms={props.coms}
labels={props.labels}
addOptions={props.addOptions}
setDisable={props.setDisable}
selectedItem={props.selectedItem}
/>
<div>
{
props.showItems.map((item, index) => {
return (
<InputFieldComponent
// setDisable={props.setDisable}
onChangeText={(e) => props.handleChange(e, item)}
enableAllButtons={props.enableAllButtons}
key={index}
item={item}
labels={props.labels}
texts={props.texts}
/>
)
})
}
</div>
</div>
</div>
</div>
)
}
InputFieldComponent.jsx
export default class InputFieldComponent extends React.Component {
setWrapperRef = (node) => {
this.wrapperRef = node;
}
render() {
const { labels, item, onChangeText, texts } = this.props
return (
<div>
<textarea
className="txt-box"
ref={this.setWrapperRef}
onChange={onChangeText}
placeholder={labels[item]}
value={texts[item]} />
</div>
)
}
}

react js delete handler removes the 1st index in the array

The problem is any item button click will delete the 1st index item in the array.
I looked at these resources on handling deleting an item in an array in react.
How to remove item in todo list using React
Removing element from array in component state
React Binding Patterns
I've tried changing how my handler is called in TodoList and TodoItemLIst and that causes the handler not to fire on click. I've tried different methods of binding the handler - adding a param has no effect on it -bind(this) breaks it & isn't necessary because I'm using a function.
I've tried setting state different ways using a filter method. No change happens...
this.setState((prevState) => ({
todoItems: prevState.todoItems.filter(i => i !== index)
}));
I'm not understanding where/what the problem is.
class App extends Component {
constructor(props) {
super(props);
this.state = {
value: '',
listItemValue: props.value || '',
todoItems: [
{id: _.uniqueId(), item: 'Learn React.'},
{id: _.uniqueId(), item: 'Improve JS skills.'},
{id: _.uniqueId(), item: 'Play with kittens.'}
]
};
}
handleChange = (event) => {
let value = event.target.value;
this.setState({
value: this.state.value,
listItemValue: value
});
}
handleSubmit = (event) =>{
event.preventDefault();
this.setState({
value: '',
listItemValue: ''
});
}
addTodoItem = () => {
let todoItems = this.state.todoItems.slice(0);
todoItems.push({
id: _.uniqueId(),
item: this.state.listItemValue
});
this.setState(prevState => ({
todoItems: [
...prevState.todoItems,
{
id: _.uniqueId(),
item: this.state.listItemValue
}]
}))
};
deleteTodoItem = (index) => {
let todoItems = this.state.todoItems.slice();
todoItems.splice(index, 1);
this.setState({
todoItems
});
}
render() {
return (
<div className="App">
<h1>Todo List</h1>
<TodoListForm name="todo"
onClick={ ()=>this.addTodoItem() }
onSubmit={ this.handleSubmit }
handleChange={ this.handleChange }
value={ this.state.listItemValue } />
<TodoList onClick={ ()=>this.deleteTodoItem() }
todoItems={ this.state.todoItems }/>
</div>
);
}
}
const TodoList = (props) => {
const todoItem = props.todoItems.map((todo) => {
return (
<TodoListItem onClick={ props.onClick }
key={ todo.id }
id={ todo.id }
item={ todo.item }/>
);
});
return (
<ul className="TodoList">
{todoItem}
</ul>
);
}
const TodoListItem = (todo, props) => {
return (
<li className="TodoListItem">
<div className="TodoListItem__Item">{todo.item}
<span className="TodoListItem__Icon"></span>
<button onClick={ todo.onClick }
type="button"
className="TodoListItem__Btn">×</button>
</div>
</li>
)
};

In the deleteTodoItem method, try just
let todoItems = this.state.todoItems.slice(0, -1);
and remove the call to splice().