Develop Reference

Rendering Child Component from store

I have a component which has child components, i want to render these child components with different Ids. They are getting their data from store.The problem is they are rendered but with the same item. how can this be solved?
MultiImages Component
const MultiImages: () => JSX.Element = () => {
const values = ['500', '406', '614'];
return (
<div>
{values.map((val, index) => {
return <OneImage key={index} projectID={val} />;
})}
</div>
);
};
export default MultiImages;
OneImage Component
const OneImage: () => JSX.Element = ({ projectID }) => {
const projectData = useProjectDataStore();
const { getProject } = useAction();
useEffect(() => {
getProject(projectID ?? '');
}, []);
return (
<>
<div>
<img
src={projectData.picture}
}
/>
<div>
<a>
{projectData.projectName}
</a>
</div>
</div>
</>
);
};
export default OneImage;

Your issue here - you are calling in a loop, one by one fetch your projects, and each call, as far as we can understand from your example and comments override each other.
Your are doing it implicitly, cause your fetching functionality is inside your Item Component OneImage
In general, the way you are using global state and trying to isolate one from another nodes is nice, you need to think about your selector hook.
I suggest you, to prevent rewriting too many parts of the code, to change a bit your selector "useProjectDataStore" and make it depended on "projectID".
Each load of next project with getProject might store into your global state result, but instead of overriding ALL the state object, you might want to use Map(Dictionary) as a data structure, and write a result there and use projectID as a key.
So, in your code the only place what might be change is OneImage component
const OneImage: () => JSX.Element = ({ projectID }) => {
// making your hook depended on **projectID**
const projectData = useProjectDataStore(projectID);
const { getProject } = useAction();
useEffect(() => {
// No need of usage **projectID** cause it will inherit if from useProjectDataStore
getProject();
}, []);
return (
<>
<div>
<img
src={projectData.picture}
}
/>
<div>
<a>
{projectData.projectName}
</a>
</div>
</div>
</>
);
};
export default OneImage;
And inside of your useProjectDataStore store result into a specific key using projectID.

Your component OneImage will return what's in the return statement, in your case:
<>
<div>
<img
src={projectData.picture}
/>
<div>
<a>
{projectData.projectName}
</a>
</div>
</div>
</>
This tag <></> around your element is a React.fragment and has no key. This is the reason you get this error.
Since you already have a div tag wrapping your element you can do this:
<div key={parseInt(projectID)}>
<img
src={projectData.picture}
/>
<div>
<a>
{projectData.projectName}
</a>
</div>
</div>
You can also change the key to Math.floor(Math.random() * 9999).
Note that passing the prop key={index} is unnecessary, and is not advised to use index as keys in a react list.

How can I make useEffect not return the initial value? I keep getting empty array when I'm trying to pass an array of objects into a component

I'm trying to pass in an array of registered users into a component, however I can't because it always renders the initial empty array before actually rendering the correct content. I've tried using useRef and it still does not work.
const Home = () => {
const nav = useNavigate()
const [userList, setUserList] = useState([]);
const [loggedInUser, setLoggedInUser] = useState({});
const [currentChat, setCurrentChat] = useState(undefined);
const [showMenu, setShowMenu] = useState(false);
useEffect(() => {
const setLoggedIn = async() => {
if (!localStorage.getItem('loggedInUser')) {
nav('/');
} else {
setLoggedInUser(await JSON.parse(localStorage.getItem('loggedInUser')))
}
}
setLoggedIn().catch(console.error);
}, [])
useEffect(() => {
const fetchUsers = async () => {
const data = await axios.get(`${allUsersRoute}/${loggedInUser._id}`);
setUserList(data.data);
}
fetchUsers().catch(console.error);
}, [loggedInUser._id])
console.log(userList);
return (
<div id='container'>
<div id='sidebar'>
<div>
<div id='home-header'>
<h1>DevsHelp</h1>
</div>
<Userlist props={userList}/>
</div>
</div>
)};
And here is the component I'm trying to render.
const Userlist = (props) => {
return (
<div>
<div id='home-header'>
<h1>DevsHelp</h1>
</div>
<div id='userlist'>
{props.map((prop) => {
{console.log(props.length)}
return (
<div className='user'>
<h3>{prop.username}</h3>
</div>
)
})}
</div>
</div>
)}
export default Userlist;
So basically, react returns .map is not a function, and I assume it's because the array goes in empty. I'm fairly new to React, so if anyone could help me, I would greatly appreciate it. Thanks!

The problem is that you are mapping over the props object, not the userList.
Try to do the following:
const Userlist = (props) => {
return (
<div>
<div id='home-header'>
<h1>DevsHelp</h1>
</div>
<div id='userlist'>
// use props.users.map instead of props.map
{props.users.map((user) => {
return (
<div className='user'>
<h3>{user.username}</h3>
</div>
)
})}
</div>
</div>
)}
export default Userlist;
and at Home component change the props of UserList to users, just to avoid confusion
<Userlist users={userList}/>

I wouldn't name props for a component "props", really:
<Userlist props={userList}/>
If you really want to, then at least inside Userlist, you would need to refer to the props object:
props.props.map...
Name your props to something that make sense to you, like for example "users". Then call props.users.map(user => {...})
A React component can take many props. When you want to access them inside the component, you need to do so by name. In your case, you defined Userlist like this:
function Userlist(props){...}
In this case, all props would have to be accessed via the props object. You defined a props value inside this object when you called <Userlist props={userList]} />
Personally, I always destructure props when I define a new component, like this:
function Userlist({users}) {...}
As a side note, your code would have worked if you had destructured the props object: function Userlist({props}) {...} This would be the smallest change you could do to make the code work, I guess. But again, I would not use "props" as a name for a prop.

How do I stop duplication of an object in localStorage?

I've a component call KeywordLocation.js, and It has one prop named location.
this component is a mapped array and on click I want to save the object of location in localStorage. I created here an empty array and pushing the object on every click. For now I'm getting 5 mapped location objects. when I click on any of them, it saves the object but on 2nd click it doesn't stop duplicating the object. How do I stop this duplication?
searchedLocation.map((location, i) => {
return (
<KeywordLocation
setShowMap={props.setShowMap}
location={location}
key={i}
getPositionFromManualSearch={props.getPositionFromManualSearch}
/>
);
});
KeywordLocation.js
const Component = ({ location }) => {
let allSearchedLocations = [];
const redirectToMap = async () => {
allSearchedLocations.push(location);
allSearchedLocations = allSearchedLocations.concat(
JSON.parse(localStorage.getItem("recent_location_searched") || "[]")
);
const previousLocation = JSON.parse(
localStorage.getItem("recent_location_searched")
);
console.log(previousLocation);
localStorage.setItem(
"recent_location_searched",
JSON.stringify(allSearchedLocations)
);
};
return (
<div onClick={() => redirectToMap()} className="pt-md cursor-pointer">
<p>{location.structured_formatting.main_text}</p>
<p className="text-xs border-b border-black pb-md ">
{location.description}
</p>
</div>
);
};

Are you entirely sure the duplication is ocurring on local storage?
As long as you use the same key, recent_location_searched, there will be only one value stored on that key. Take a look at the "Storage" tab on your browser's debug console to see what's actually being stored.
All evidence seems to point that the duplication is ocurring at the searchLocations variable, not atlocalStorage.
You might try to add some conditional logic that prevents you from pushing to searchLocations if the location is the same as the one on the last item on the array.

The problem is not related to localStorage but more about the usage of the array structure. You could rely on JavaScripts object to store the unique values. You lose the insertion order but you can create a companion array that keep a reference to the order.
const Test = ({ location }) => {
const redirectToMap = () => {
const locations =
JSON.parse(localStorage.getItem("recent_location_searched")) || {};
locations[location.name] = location;
localStorage.setItem("recent_location_searched", JSON.stringify(locations));
};
return (
<div onClick={() => redirectToMap()} className="pt-md cursor-pointer">
<p>{location.name}</p>
</div>
);
};
export default function App() {
const data =
JSON.parse(localStorage.getItem("recent_location_searched")) || {};
return (
<div>
<div className="App">
{[
{ name: "location1" },
{ name: "location3" },
{ name: "location2" }
].map((location) => (
<Test key={location.name} location={location} />
))}
</div>
<ul>
{Object.values(data).map((location) => (
<li key={location.name}>Saved {location.name}</li>
))}
</ul>
</div>
);
}

How to append a dynamic HTML element to React component using JSX?

I'm new to Reactjs. I'm creating an App with a Survey creation like Google Forms. My component has a button to create a new Div with some HTML elements to create a survey question. To do that, on the button click function, I'm creating a JSX element and push it to an array. And then, I set the array inside the render function to display what inside it.
The problem is, Even though the Array is updating, the dynamic HTML part can not be seen on the page. The page is just empty except the button. How can I fix this?
Component:
import '../../styles/css/surveycreation.css';
import React, { Component } from 'react';
let questionId = 0;
class SurveyCreation extends Component {
constructor(props) {
super(props);
this.questionsList = [];
this.state = {
}
}
addQuestion = (e) => {
e.preventDefault();
questionId = questionId + 1;
this.questionsList.push(
<div key={questionId}>
question block
</div>
)
}
render() {
return (
<div>
<button onClick={e => this.addQuestion(e)}>Add Question</button>
<div>
{this.questionsList}
</div>
</div>
);
}
};
export default SurveyCreation;

The only way a react component knows to rerender is by setting state. So you should have an array in your state for the questions, and then render based on that array. In the array you want to keep data, not JSX elements. The elements get created when rendering.
constructor(props) {
super(props);
this.state = {
questions: [],
}
}
addQuestion = () => {
setState(prev => ({
// add some object that has the info needed for rendernig a question.
// Don't add jsx to the array
questions: [...prev.questions, { questionId: prev.questions.length }];
})
}
render() {
return (
<div>
<button onClick={e => this.addQuestion(e)}>Add Question</button>
<div>
{this.state.questions.map(question => (
<div key={question.questionId}>
</div>
)}
</div>
</div>
);
}

I think you're component is not re-rendering after you fill the array of elements.
Try adding the questionsList to the component's state and modify your addQuestion method so that it creates a new array, finally call setState with the new array.

You need to map your this.questionsList variable.
You can save the 'question string' in the array and then iterate the array printing your div..
Something like this.
<div>
{this.state.questionsList.map(questionString, i => (
<div key={i}>
{questionString}
</div>
)}
</div>

React returns older state value onClick

I am adding a component onclick and keeping track of the components using useState Array. However when I go to remove one of the added components, it doesn't recognize the full component Array size, only the state that was there when that component was initially added.
Is there a way to have the current state recognized within that delete function?
https://codesandbox.io/s/twilight-water-jxnup
import React, { useState } from "react";
export default function App() {
const Span = props => {
return (
<div>
<span>{props.index}</span>
<button onClick={() => deleteSpan(props.index)}>DELETE</button>
Length: {spans.length}
</div>
);
};
//set initial span w/ useState
const [spans, setSpans] = useState([<Span key={0} index={Math.random()} />]);
//add new span
const addSpan = () => {
let key = Math.random();
setSpans([...spans, <Span key={key} index={key} />]);
};
//delete span
const deleteSpan = index => {
console.log(spans);
console.log(spans.length);
};
//clear all spans
const clearInputs = () => {
setSpans([]);
};
return (
<>
{spans}
<button onClick={() => addSpan()}>add</button>
<button onClick={() => clearInputs()}>clear</button>
</>
);
}

UPDATE - Explaining why you are facing the issue descibed on your question
When you are adding your new span on your state, it's like it captures an image of the current values around it, including the value of spans. That is why logging spans on click returns you a different value. It's the value spans had when you added your <Span /> into your state.
This is one of the benefits of Closures. Every <Span /> you added, created a different closure, referencing a different version of the spans variable.
Is there a reason why you are pushing a Component into your state? I would suggest you to keep your state plain and clean. In that way, it's also reusable.
You can, for instance, use useState to create an empty array, where you will push data related to your spans. For the sake of the example, I will just push a timestamp, but for you might be something else.
export default function App() {
const Span = props => {
return (
<div>
<span>{props.index}</span>
<button onClick={() => setSpans(spans.filter(span => span !== props.span))}>DELETE</button>
Length: {spans.length}
</div>
);
};
const [spans, setSpans] = React.useState([]);
return (
<>
{spans.length
? spans.map((span, index) => (
<Span key={span} index={index} span={span} />
))
: null}
<button onClick={() => setSpans([
...spans,
new Date().getTime(),
])}>add</button>
<button onClick={() => setSpans([])}>clear</button>
</>
);
}
I hope this helps you find your way.