So I'm using React and I made a little code that has a textbox with a submit button, and when something is typed in and submitted, it creates a tweet with the text I typed in and some pre-made elements as you see here:
[1]: https://i.stack.imgur.com/pvfSf.png
The random letters with the Like and Delete buttons is what I submitted each time.
What I'm confused is why every single tweet gets deleted when I use this code:
const deleteTweet = () =>{
setTweets(tweets.filter(tweet => tweet !== tweet))
}
But when I use this code, only the one specific tweet I clicked Delete on, gets removed:
const deleteTweet = () =>{
setTweets(tweets.filter(t => t !== tweet))
}
The 'tweet' after the !== is a prop I'm passing down.
You have a conflict between tweet used as parameter on map and tweet used as props, Javascript's scoping take the latest variable which is the map's tweet.
So when you put tweet on map function it overrides the props tweet.
You may take a look at closures : https://developer.mozilla.org/en-US/docs/Web/JavaScript/Closures
Related
I have a problem trying to update an array in a setState.
First of all, I have an array in the main component called "myCourses", that have the information about the courses from a student. Then, I have a modal component, which opens after a click event. The modal receives "myCourses" from main and modify when some conditions are true, and the array is updated.
The problem occurs after the setStateMyCourses in modal component, because the cards only renders once, after a few intents with the same patron (open the modal, do the same things and the courses not changes visually, when in the first intent the element is removed).
Here I detach some code of the project.
Main component:
const [myCourses, setMyCourses] = useState([]);
UseEffect(() => {
...
loadMyCourses(setMyCourses)
...
},[]);
...
{myCourses.map((item) => {Card name = {item.name}}
...
{condition && <ModalComponent myCourses={myCourses} setMyCourses={setMyCourses}/>}
In ModalComponent I have the following:
...
const myCoursesAux = myCourses
myCoursesAux.splice(index, 1);
setMyCourses([...myCoursesAux]);
...
You should never mutate state directly, instead use the updater function form of setState to modify the array without mutating it. Have a look at this documentation for reference
setMyCourses(prev => prev.filter((_,i) => i !== index))
Sorry for the dealy, and thanks again for the reply. I found the problem yesterday. The problem was in the first condition when I call for the modal component.
I am having trouble preventing unnecessary side-effects from a useEffect hook linked to a component that gets re-rendered/reused multiple times after being clicked. I want the side-effect to trigger an action once, but it is being triggered for every render.
I'm building a task viewer that displays nested task data. Please see screenshot #1 for reference.
For context, the main display shows the main tasks (see Event Data) and renders a clickable button if the task has sub-events. When this button is clicked, the selected main task is displayed at the top of the hierarchy view (see Event Hierarchy) and its sub-events are displayed below the hierarchy in a separate pane (see Event Details).
Like the main tasks, if these sub-events in 'Event Details' have their own sub-events, they are also rendered with a clickable button. When this sub-event button is clicked, this clicked sub-event is added to the bottom of the hierarchy, where the clicked main task is already displayed in bold. This selected sub-event's sub-events then replace the content in the 'Event Details' pane.
As the user clicks through the nested data, the clicked sub-event is added to the bottom of the hierarchy so that the user has an idea of where he is in the nested data and its sub-events displayed in 'Event Details'. All 'Event Hierarchy' and 'Event Details' data is cleared when the user selects a new main event or selects a new page.
The hierarchy events are held in an array managed via useState and every time another sub-event is clicked, it is added to this array. That's the idea, at least.
#1
My problem is this:
If I place my setHierarchy function inside a useEffect hook with the selectedTask as dependency, it renders the selectedTask in the hierarchy instantaneously, but the button component that triggers setHierarchy is re-rendered for every sub-event being displayed in 'Event Details' (as I want each event to be clickable) and in doing so, it adds that many copies of the event to my hierarchy array. This happens even though I am checking to see if the hierarchy array already contains the selected subevent before adding it. See result in screenshot #2.
I have tried various configurations of checking the array, but I cannot seem to stop it from adding these copies to and subsequently displaying them in the Hierarchy.
If I place the setHierarchy function inside my click handler, only one single event is added, but it executes before the selectedSubEvent has been updated. This means the hierarchy array is empty upon first render and stays one click 'behind' ie. a specific event is only displayed upon the following click event, after the click that selected it.
#2
This is all done inside my ExpandSubEvents button component (see code below) and also managed via a context provider.
I have tried moving the setHierarchy into a separate function, inside a useCallback, and triggering it from both the clickHandler and the useEffect that sets the selectedSubEvent. This did not resolve the issue.
I've also tried useRef to try and link it to the latest state. I'm not sure that's even doable/correct.
What am I doing wrong here? I am fairly new to coding, so any input on this would be much appreciated.
Sidenote: I suspect that my setup is perhaps beyond the intended scope of useContext. Is it? What can I do to make improvements? Is this perhaps in any way responsible for my issue?
Thank you for taking your time to read this far. I appreciate it!
Deon
ExpandSubEvents Component
import React, { useCallback, useContext, useEffect, useMemo } from 'react';
import SubEventContext from '../../store/sub-event-context';
import classes from './ExpandSubEvents.module.css';
const ExpandSubEvents: React.FC<{
id: number;
subEvents: number;
}> = React.memo((props) => {
// Extract context
const subEventCtx = useContext(SubEventContext);
const {
subEvents,
subEventParentId,
selectedSubEvent,
hierarchy,
setSubEventParentId,
setFetchId,
setSelectedSubEvent,
setHierarchy,
} = subEventCtx;
// Get id of event for when it is clicked
const id = React.useMemo(() => props.id, [props.id]);
let eventIds: number[] = useMemo(() => [], []);
if (hierarchy) {
for (const event of hierarchy) {
eventIds.push(event.id);
}
}
// Set CSS classes to style button if it has sub-events
let subEventQuantity = props.subEvents;
let importedClasses = `${classes['sub-event-button']}`;
if (subEventQuantity === 0) {
importedClasses = `${classes['no-sub-events']}`;
}
// Push the event to the Hierarchy display
// NOTE Tried moving the setHierarchy to a separate function, but it did not make a difference
// const triggerHierarchy = useCallback(() => {
// if (!eventIds.includes(id))
// setHierarchy((prevState) => [...prevState, ...selectedSubEvent]);
// }, [eventIds, id, selectedSubEvent, setHierarchy]);
// Respond to subevent button click event
const clickHandler = useCallback(() => {
setSubEventParentId(id);
setFetchId(id);
// This setHierarchy works, but executes before the selectedSubEVent has been updated
// Furthermore, if a new subevent is selected, it checks if the NEW clicked one has been added
// BUT sends the OLD event still in selectedSubEvent to the hierarchy before IT has been updated
// meaning that the check does not stop the same event being added twice
if (!eventIds.includes(id))
setHierarchy((prevState) => [...prevState, ...selectedSubEvent]);
}, [
eventIds,
id,
selectedSubEvent,
setFetchId,
setHierarchy,
setSubEventParentId,
]);
// NOTE Tried useRef to get setHierarchy to use the latest selectedSubEvent
// const subEventRef = useRef<Event[]>([]);
// subEventRef.current = hierarchy;
// Trying to setHierarchy directly from its own useEffect
// useEffect(() => {
// if (!eventIds.includes(id))
// setHierarchy((prevState) => [...prevState, ...selectedSubEvent]);
// }, [eventIds, hierarchy, id, selectedSubEvent, setHierarchy]);
// Filter the event from the subEvent array and set it to selectedSubEvent
useEffect(() => {
setSelectedSubEvent(
subEvents.filter((subEvent) => subEvent.id === subEventParentId)
);
}, [setSelectedSubEvent, subEventParentId, subEvents]);
return (
<button onClick={clickHandler} className={importedClasses}>
{subEventQuantity}
</button>
);
});
export default ExpandSubEvents;
Hi,
so I've redacted some sensitive information from the screen shot, but you can see enough to see my problem.
Now, I'm trying to build the UI for a site that gets data from a weather station.
I'm trying to use react-google-maps' InfoBox, which disables mouse events by default.
It seems that to enable mouse events, you must wait until the DOM is loaded, and then add the event handlers.
react-google-maps' InfoBox fires an onDomReady event (perhaps even upon adding more divs) but seems to never fire an onContentChanged event (I've looked in the node_modules code).
The content I'm putting in the InfoBox is basically a div with a string ref for each type of weather data. Sometimes there comes along a new type of weather data so I want to put that in also, and have the ref be available / usable.
However, immediately after the new divs have been added (and the DOM has been updated to show them), when I try to console log the DOM nodes (the refs refer to the nodes because they are divs and not a custom built component) the latest added ones are undefined.
They do become a div (not undefined) a few renders later.
I've contemplated that this may be because
1) the DOM is not being updated before I'm trying to access the refs, but indeed the UI shows the new divs,
2) string refs are deprecated (React 16.5),
but they work for the divs in comonentDidMount and eventually for new divs in componentDidUpdate,
3) executing the code within the return value of render may be run asynchronously with componentDidMount, but I also tried setTimeout with 3000 ms to the same effect,
4) of something to do with enumerable properties, but getOwnProperties behaves the same way.
In the end I decided I'll console log this.refs and Object.keys(this.refs) within the same few lines of code (shown in the screen shot), and you can see that within one console log statement (where Object.keys was used in the previous line) that while this.refs is an object with 8 keys, the two most recently added refs don't appear in Object.keys(this.refs).
This is probably a super complex interaction between react-google-maps' InfoBox, React's refs, and JavaScript's Object.keys, but it seems like it should be simple and confuses me to a loss.
Can anyone shed some light on why this might be happening??
The code looks something alike:
class SensorInfoWindow extends React.Component {
handleIconClick = () => {
// do stuff here
}
componentDidMount() {
this.addClickHandlers();
}
componentDidUpdate() {
this.addClickHandlers();
}
addClickHandlers = () => {
const keys = Object.keys(this.refs);
for(let i=0; i<keys.length; i++) {
const key = keys[i];
let element = this.refs[key];
if (element !== undefined)
element.addEventListener('click', this.handleIconClick);
}
}
render() {
const { thissensor, allsensors } = this.props;
let divsToAddHandlersTo = [];
const sensorkeys = Object.keys(allsensors);
for (let i=0; i<sensorkeys.length; i++) {
divsToAddHandlersTo.push(
<div
ref={'stringref' + i}
/>
{/* children here, using InfoBox */}
</div>
);
}
return (
<div>
{divsToAddHandlersTo}
</div>
);
}
}
This is, in essence, the component.
I know there are some similar topics but none seems to be in the same direction of what I'm trying to do, thus a new thread.
I have a component that displays a list of keys, each with a checkbox attached to the string. In addition, I have a button that supposedly calls an API with all keys selected and delete these keys.
Several things I'm trying to achieve:
checking a check box enables the delete button
click the delete button should send a POST to API, the list should then reload
Since the list is reloaded, all checkbox should be unselected, thus the delete button is once again disabled
there's another button outside of this function that checks for the length of the list as well, which I don't know how to associate with this list if I fetch the list in the component.
I'm facing the problem which I don't know how to make the button and the checkboxes associate to each other. I tried using state with a checked state, which is a boolean, but that's only one boolean and cannot record several keys. I think using an array would work? Then again I'm not sure how to properly append or remove the key checked.
my code looks like
class AppList extends Component {
constructor() {
super();
this.state = {
checked: [],
apps: []
};
this.handleChecked = this.handleChecked.bind(this);
}
componentDidMount() {
fetch("some_url", {
method: 'post',
body: JSON.stringify({"user": "some_email"}),
headers: {'Content-Type': ' application/json'}
})
.then(res => res.json())
.then(
(result) => {
this.setState({apps: JSON.parse(result)});
},
(error) => {
console.log("error", error);
}
);
}
handleDeleteKey = (event) => {
// fetch(I'll worry about this later)
this.setState({checked: false});
console.log("delete!!!!");
}
handleChecked () {
this.setState({checked: !this.state.checked});
}
render () {
const apps = this.state.apps.map((app) =>
<div>
<input type="checkbox" onChange={this.handleChecked} />
{` ${app}`}
</div>
);
return (
<div>
<h4>Client Key List:</h4>
{this.state.apps.length > 0 ? <ul>{apps}</ul> : <p>No Key</p>}
{this.state.apps.length > 0 ? <button className="api-instruction-button" onClick={this.handleDeleteKey}>Delete Selected Key(s)</button> : null}
</div>
);
}
}
export default AppList;
I feel like my design is completely wrong but I don't know how to fix it. It seems like there are so many states to be passed around and nothing is the outermost, almost a cyclic dependency.
Anyone had any experience dealing with this problem? It seems like it's a common user action but I can't figure it out.
EDIT: after digging it a bit more, it seems like I need to call componentDidMount outside of the AppList. It should be in the component that uses AppList, let's call it MainApp.
MainApp calls componentDidMount which is the same as the one in AppList. The one in AppList gets removed, and the keys are passed to AppList as props.
I have trouble handling the clicking event. It seems like the component is always updating, so if I want to append the clicked key to the array, it wouldn't work. The same call will be made again and again.
Since there's another button in MainApp that requires the list of keys, I can't just pass the call into AppList. However, updating in AppList should update the MainApp as well. How does it work? I'm so confused
EDIT2:
https://codesandbox.io/s/7w2w11477j
This recreation should contain all functions I have so far, but I can't get them to work together.
Again my task is simply:
I have a list of strings, each with a checkbox
checking the checkbox selects the specific string
There's a button that I can click to delete these entries in my db by calling an API
Is refreshing the MainApp needed in this case? Otherwise I need to delete the strings in frontend so they don't display after the delete button is pressed
Here's what I believe you were going for: https://codesandbox.io/s/w23wv002yw
The only problem that made yours not work properly was you were just getting a little jumbled with where to put everything.
Contents:
The MainApp.js will only contain the apps and a method for deleting them in the backend. Other than those two methods, nothing else really concerns the MainApp.js file.
The AppList.js will contain all the methods that update its own checked state, the delete button itself, and a method to clear the checked state on delete.
Processes:
First, MainApp.js will load and remount with a backend api pull and populate its apps state. Once it's finished that, it will pass it on to AppList.js. From there, AppList.js will render that list as a multi-select field onscreen. The user can then select or deselect any of the options. As an option is selected, its index is pushed to the checked state and organized in ascending order.
(ordering the array isn't that necessary, but I figured it would help if you wanted to retool it sometime down the road)
When one or more option is selected, a delete button will appear. When the user clicks the delete button, AppList.js will call the delete function passed to it from MainApp.js, then it will clear the current checked state.
How can I manually update DraftJs's ContentState in response to clicked text?
I have a list of text item. When one is clicked I am passing that text down to Draftjs, but because I am setting the state using componentWillReceiveProps() it requires that I click the text twice to get an update.
componentWillReceiveProps() {
const activeNoteText = this.props.activeNoteText;
if (activeNoteText !== '') {
this.setState({ editorState: EditorState.createWithContent(ContentState.createFromText(activeNoteText)) });
}
}
First click: Update the App state and pass props down to Draftjs (component updates before receiving new props)
Second click: Now the prop is properly set and Draftjs updates (component updates with the props received on the first click)
How can I accomplish this in one pass? I know there's no componentDidReceiveProps and I know there's a good reason, though I can't claim to fully understand yet, so what's the best practices way to accomplish something like this?
Why are you using componentwillReceiveProps?.
What you can do, is have the states your setting in Draftjs i.e. editorState(Well, that's what I can make out) in its parent and whenever a list item is clicked on the click handler for that update the editorState and then pass it as props to Draft js.
Further for the condition, where you are checking if it is not empty,
You could use the
getInitialState(){
.....
}
For initialization when your component is initially loaded. So you could have a default value for editorState.