Develop Reference

Visit each child in props.children and trigger a function

I want to be able to visit the children <Textfield> of my form <Form> upon submit.
In each child hook object, I also want to trigger a certain function (eg., validate_field). Not sure if this possible in hooks? I do not want to use ref/useRef and forwardRef is a blurred concept to me yet (if that's of any help).
My scenario is the form has been submitted while the user did not touch/update any of the textfields so no errors were collected yet. Upon form submit, I want each child to validate itself based on certain constraints.
I tried looking at useImperativeHandle too but looks like this will not work on props.children?
Updated working code in:
https://stackblitz.com/edit/react-ts-jfbetn
submit_form(evt){
props.children.map(child=>{
// hypothetical method i would like to trigger.
// this is what i want to achieve
child.validate_field() // this will return "is not a function" error
})
}
<Form onSubmit={(e)=>submit_form(e)}
<Textfield validations={['email']}>
<Textfield />
<Textfield />
</Form>
Form.js
function submit_form(event){
event.preventDefault();
if(props.onSubmit){
props.onSubmit()
}
}
export default function Form(props){
return (
<form onSubmit={(e)=>submit_form(e)}>
{props.children}
</form>
)
}
So the Textfield would look like this
…
const [value, setValue] = useState(null);
const [errors, setErrors) = useState([]);
function validate_field(){
let errors = []; // reset the error list
props.validations.map(validation => {
if(validation === 'email'){
if(!some_email_format_validator(value)){
errors.push('Invalid email format')
}
}
// other validations (eg., length, allowed characters, etc)
})
setErrors(errors)
}
export default function Textfield(props){
render (
<input onChange={(evt)=>setValue(evt.target.value)} />
{
errors.length > 0
? errors.map(error => {
return (
<span style={{color:'red'}}>{error}</span>
)
})
: null
}
)
}

I would recommend moving your validation logic up to the Form component and making your inputs controlled. This way you can manage the form state in the parent of the input fields and passing in their values and onChange function by mapping over your children with React.cloneElement.
I don't believe what you're trying to do will work because you are trying to map over the children prop which is not the same as mapping over say an array of instantiated child elements. That is to say they don't have state, so calling any method on them wouldn't be able to give you what you wanted.
You could use a complicated system of refs to keep the state in your child input elements, but I really don't recommend doing that as it would get hairy very fast and you can just solve the issue by moving state up to the parent.
simplified code with parent state:
const Form = ({ children }) => {
const [formState, setFormState] = useState(children.reduce((prev, curr) => ({ ...prev, [curr.inputId]: '' }), {}));
const validate = (inputValue, validator) => {}
const onSubmit = () => {
Object.entries(formState).forEach(([inputId, inputValue]) => {
validate(
inputValue,
children.filter(c => c.inputId === inputId)[0].validator
)
})
}
const setFieldValue = (value, inputId) => {
setFormState({ ...formState, [inputId]: value });
};
const childrenWithValues = children.map((child) =>
React.cloneElement(child, {
value: formState[child.inputId],
onChange: (e) => {
setFieldValue(e.target.value, child.inputId);
},
}),
);
return (
<form onSubmit={onSubmit}>
{...childrenWithValues}
</form>
)
};
const App = () =>
<Form>
<MyInput validator="email" inputId="foo"/>
<MyInput validator="email" inputId="foo"/>
<MyInput validator="password" inputId="foo"/>
</Form>
I still don't love passing in the validator as a prop to the child, as pulling that out of filtered children is kinda jank. Might want to consider some sort of state management or pre-determined input list.

How to properly use React.creatRef()

I've been beating my head against the wall and cross referencing code I've read from others and questions that have been asked. I'm at the point where I know I'm just not looking in the right direction, however I'm not sure where to turn.
The app I'm writing was originally written by me in 2019, and I did not know of React h
Hooks as I learned components from a coding bootcamp. TL;DR: I'm rusty.
The issue:
I'm trying to use AXIOS to use a PUT call into my MongoDB, and the way I learned was by using refs. Refs in the way I learned is now deprecated, and I just want to get this working so I can move on to another project and start using Hooks instead.
When I use my button created to save the change, I get an error in the browser console, however it refreshes too fast for me to catch the exact error. The second I get to look at the wall of text, it looks similar to a bad promise, but I'm not entirely sure. Either way, the data does not get updated.
My code:
import React, { Component } from 'react'
import axios from 'axios'
export default class EditSeed extends Component {
constructor(props){
super(props)
this.state = {
_id: '',
seed: '',
created_at: '',
__v: ''
}
this.changeHandler = this.changeHandler.bind(this)
this.myRef = React.createRef
this.focusTextInput = this.focusTextInput.bind(this);
}
focusTextInput() {
// Explicitly focus the text input using the raw DOM API
// Note: we're accessing "current" to get the DOM node
this.textInput.current.focus();
}
componentDidMount(){
this.fetchSeed()
}
fetchSeed = async () => {
try {
const res = await axios.get(`/api/grapevine/${this.props.match.params.id}`)
this.setState({
_id: res.data._id ,
seed: res.data.seed,
created_at: res.data.created_at,
__v: res.data.__v
})
}
catch (err) {
this.setState({ error: err.message })
console.log(err)
}
}
editSeed = async (newSeed) => {
try {
const res = await axios.request({
method: 'put',
url: `/api/grapevine/${this.state._id}`,
data: newSeed
})
res.this.props.history.push(`/`)
}
catch (err) {
this.setState({ error: err.message })
console.log(err)
}
}
onSubmit = (e) => {
const newSeed = {
seed: this.myRef.current.seed.value,
created_at: this.myRef.current.created_at.value
}
this.editSeed(newSeed)
e.preventDefault()
}
changeHandler = (e) => {
const target = e.target
const value = target.value
const name = target.name
this.setState({
[name]: value
})
}
render(){
return(
<div>
<h1>Edit Seed</h1>
<form onSubmit={this.onSubmit.bind(this)}>
<label>
Edit Message:
<input type="text" name="seed" ref={this.myRef} value={this.state.seed} onChange={this.changeHandler} />
</label>
<input type="submit" value="Save" />
</form>
</div>
)
}
}
My fetch function works as intended, it's mainly just the edit that doesn't want to work. I have tried changing
<input type="text" name="seed" ref={this.myRef} value={this.state.seed} onChange={this.changeHandler} />
to
<input type="text" name="seed" ref={this.myRef.current} value={this.state.seed} onChange={this.changeHandler} />
Obviously I am doing something wrong, and I have referenced and read the React docs on this about 10 times and I'm really just hitting a wall.
Any insight would be massively appreciated.

Firstly, React.createRef is a function, so it needs to be invoked.
this.myRef = React.createRef();
Then you simply attach the ref to the element.
<input
ref={this.myRef}
type="text"
name="seed"
value={this.state.seed}
onChange={this.changeHandler}
/>
Then whenever you need to reference the input's ref you access the current value of it.
this.myRef.current
Update
I don't think the React ref is providing much for you here since you duplicate the seed and created_at into local state. You update the seed state via the onChange handler. Why not just forego the ref and access the state in the submit handler. I believe this will resolve your "cannot access value of undefined" error since the input element target object likely doesn't have seed or created_at attributes to access a value of.
onSubmit = (e) => {
e.preventDefault();
const newSeed = {
seed: this.state.seed,
created_at: this.state.created_at // is this supposed to be a current datetime?
}
this.editSeed(newSeed);
}
changeHandler = (e) => {
const { name, value } = e.target;
this.setState({
[name]: value
});
}

You did nearly got it right, just a few minor changes will lead you to the right way:
First: You need to invoke React.createRef function:
this.myRef = React.createRef -> this.myRef = React.createRef()
Second: You need to call e.preventDefault() from the begining of your handler so that the whole page will not get refeshed imediately. Something like this:
onSubmit = (e) => {
e.preventDefault();
const newSeed = {
seed: this.myRef.current.seed.value,
created_at: this.myRef.current.created_at.value
}
this.editSeed(newSeed)
}
From then, I think you will easily get to the right path.

You can use useRef hook in functional components like this:
import React, {useRef} from 'react';
function MyComponenet () {
myRef = useRef(null) // <---- initialize your ref with null
return (
<div ref=myRef >
Hello World
</div>
)
}
now you create a reference and initiate it with a null value, then passed it to the div element. from now you can manipulate your ref like get its value or assign values, click, and other actions.
with TypeScript
myRef = useRef<HTMLDivElement>(null)
if you are passing myRef to a div element, so your ref type will be HTMLDivElement

React JS search in Array (character by character)

This is my first program in React. I've as below:
import React from 'react';
import './App.css';
class App extends React.Component {
constructor(props) {
super(props)
this.state = {
name : ''
}
}
render() {
return (
<>
<div>
<label for="searchEmp">Search Person: </label>
<input type="text" value={this.state.name} id="searchEmp"
placeholder="Enter Person's Name"
onChange={event => this.setState({name: event.target.value})}/><br/>
</div>
{["John","Steve","Alen","Stephen",
"Smith","Alex","Jack","Andy","Jacky"].map(item => {
return <div>{item}</div>})}
</>
);
}
}
export default App;
In Output, I've something like as
I want to filter this list character by character. For e.g. When I enter S the list should filtered with names starting from S as below:
Next, If I enter t after S the list should contain only names as:
and so on. How can I get this? Apart, as a newbie to React, Is my code okay? Thanks in advance.

So, first of all I think the good practice would be ti either keep the list as constant one if it's fixed or some variable at class level,
Scenario you are asking for is preety much like you want to filter out the list each time, so you can filter out the list kept in variable using a function & could return the list from the function to use
let namesList = ['ab', 'fg', 'test'];
input = 'a';
let rgxp = new RegExp(input, "g");
function findFilterNames() {
return namesList.filter(x => x.match(rgxp));
}
test = findFilterNames();
console.log(test);

I'll try my best to answer but apologies in advance if this doesn't work, I've just started to learn React as well.
Whenever you use setState, the component will re-render itself, so keeping that in mind, you could use the following:
Create a function that looks for this.state.name and checks to see if its blank or has an actual value. If it does have a value, it will either use filter or map to run through the name array and return div elements with the values placed inside.
See code below:
class App extends React.Component {
constructor(props) {
super(props)
this.state = { name: '' };
}
renderNames() {
this.names =["John","Steve","Alen","Stephen","Smith","Alex","Jack","Andy","Jacky"];
if(this.state.name !== '') {
return this.names.map((name) => {
if (name.includes(this.state.name)){
return <div>{name}</div>;
}
});
} else {
return this.names.map((name) => {
return <div>{name}</div>;
});
}
}
render() {
return (
<>
<div>
<label for="searchEmp">Search Person: </label>
<input type="text" value={this.state.name} id="searchEmp"
placeholder="Enter Person's Name"
onChange={event => this.setState({name: event.target.value})}/><br/>
</div>
{this.renderNames}
</>
);
}
}

I will keep it simple and easy, you must use a function in Javascript called filter() with includes() function.
I will assume the search term that coming from the input called term, and the array that you need to filter it called names
const names = ["John","Steve","Alen","Stephen","Smith","Alex","Jack","Andy","Jacky"];
let term = "s";
const searchResults = names.filter(name => {
return name.toLowerCase().includes(term.toLowerCase());
});
// the result will be array that contain the following ["Steve","Stephen","Smith"]
when you consloe.log(searchResults) you will have ["Steve","Stephen","Smith"] because term value is "s" so you get the all names that have "s" character.
We change the array items to lowercase using toLowerCase() to avoid the case-senstive if there is character upper case
you can test the code here just put the name of the filtered searchResults at the end of the code
I see this way as the fastest way to search by character.
this is a repo as an example using Reactjs :
https://github.com/Tawfeekamr/react-search-in-array-character-by-character.git

React: UI Flickering When State Updated

I have a component that displays search data returned from the Spotify API. However, every time I update the state the UI flickers:
Input:
<DebounceInput
debounceTimeout={300}
onChange={handleChange}
/>
Hook:
const [searchResults, setSearchResults] = useState(null)
API call w/ Apollo:
const searchSpotify = async (query) => {
const result = await props.client.query({
query: SearchTracks,
variables: {
query
}
})
const tracks = result.data.searchedTracks
setSearchResults(tracks)
}
Render:
{searchResults &&
<div className="search-results">
{searchResults.map((song) => (
<SongInfo key={song.id} {...song} />
))}
</div>
}
I noticed it only happens on the first load. For example, if I were to type the query again it shows without flickering. Is there a better way to implement this so the UI doesn't flicker?

Below are the frames that cause the flicker. What I think is happening is it takes some time for the images to load. While they are loading the items have reduced height. You should make sure SongInfo layout does not depend on whether the image has been loaded or not.
Images not loaded - items are collapsed:
Images were loaded:

I think whats happening is that you are executing a search query on every key stroke which is causing the weird behavior.
Use lodash debounce to avoid doing a search on every key stroke.
That should address the flickering. (Also, adding a loading state will help)
Sample debounce component
import React, {Component} from 'react'
import { debounce } from 'lodash'
class TableSearch extends Component {
//********************************************/
constructor(props){
super(props)
this.state = {
value: props.value
}
this.changeSearch = debounce(this.props.changeSearch, 250)
}
//********************************************/
handleChange = (e) => {
const val = e.target.value
this.setState({ value: val }, () => {
this.changeSearch(val)
})
}
//********************************************/
render() {
return (
<input
onChange = {this.handleChange}
value = {this.props.value}
/>
)
}
//********************************************/
}

Double setState method in one function

I am trying to create a autocomplete component. It's an input where user types the countru name and if letters match name of some country, the hints are displayed.
In my App Component i have method handleChange Within this method i change my state two times, which is bad idea.
How can I split it to change state in distinct methods ?
import React, { Component } from 'react';
import AutoComplete from './autoComplete.jsx';
import data from './data.json';
class App extends Component {
constructor(props) {
super(props);
this.state = {
inputValue: '',
resoults: []
}
}
handleChange() {
let inputValue = this.refs.input.value;
this.setState({
inputValue: inputValue
});
let regular = "^" + this.state.inputValue;
let reg = new RegExp(regular , "i");
let filtered = data.filter((i,index)=> {
return (reg.test(i.name)
);
});
console.log(filtered);
this.setState({resoults:filtered})
}
render() {
return (
<div>
<input onChange={this.handleChange.bind(this)} type="text" ref="input"/>
<h3>You typed: {this.state.inputValue}</h3>
<AutoComplete resoults={this.state.resoults} />
</div>
);
}
}
export default App;
import React, {Component} from 'react';
class AutoComplete extends Component {
render() {
return (
<div>
<h4>autocompleteComponent</h4>
{this.props.resoults.map((i)=> {
return (
<ul>
<li>{i.name}</li>
</ul>
);
})}
</div>
);
}
}
export default AutoComplete;

I found myself in this position many times, but I got to the conclusion that it's better to compute the autocomplete options (in your case) without having them in the state of your component.
As I have used them until now, the state and props of a component should represent minimal data needed to render that specific component. Since you have your input value in the state, having the autocomplete options there also seems redundant to me. So here is what I propose:
class App extends Component {
this.state = {
inputValue: '',
};
handleChange(e) {
const inputValue = e.target.value;
this.setState({
inputValue,
});
}
computeResults() {
const {inputValue} = this.state;
// your functionality for computing results here
}
render() {
const {inputValue} = this.state;
const results = this.computeResults();
return (
<div>
<input type="text" onChange={this.handleChange.bind(this)} value={inputValue} />
<h2>You typed: {inputValue}</h2>
<Autocomplete results={results} />
</div>
);
}
}
Notes
Since your results come synchronously, via the .json import, this seems the perfect solution to me. If you want to get them via fetch or anything else, then you'll have to figure out a slightly different approach, but keep in mind that the state of your component should not contain redundant data.
Stop using ref with string value! and use refs when there is absolutely no other way because a React component should not generally deal with DOM operations directly. If you really need to use refs, use ref callbacks.
Hope this helps!

Use another function and setState callBack:
handleChange() {
let inputValue = this.refs.input.value;
this.setState(
{
inputValue: inputValue
},
() => this.secondFunc()
);
}
secondFunc() {
let regular = '^' + this.state.inputValue;
let reg = new RegExp(regular, 'i');
let filtered = data.filter((i, index) => {
return reg.test(i.name);
});
console.log(filtered);
this.setState({ resoults: filtered });
}