guys, I'm just trying to set some contact data in local storage and render on DOM but after reloading the page there is no contact data in localStorage to render in DOM!
I tried in other browsers but the result is equal.
here is my code:
import { useEffect, useState } from "react";
import { toast } from "react-toastify";
import ContactForm from "./ContactForm";
import ContactList from "./ContactList";
const ContactApp = () => {
const [contacts, setContacts] = useState([]);
const addContactHandler = (formValues) => {
if (!formValues.name || !formValues.email) {
toast.error("Name and email are required");
return;
}
setContacts([...contacts, { ...formValues, id: Date.now() }]);
};
const deleteContactHandler = (id) => {
setContacts(contacts.filter((contact) => contact.id !== id));
};
useEffect(() => {
const savedContacts = JSON.parse(localStorage.getItem("contacts"));
if (savedContacts) setContacts(savedContacts);
}, []);
useEffect(() => {
localStorage.setItem("contacts", JSON.stringify(contacts));
}, [contacts]);
return (
<div className="contact-app">
<nav>
<h1>Contact Manager</h1>
</nav>
<ContactForm onClick={addContactHandler} />
<ContactList onDelete={deleteContactHandler} contacts={contacts} />
</div>
);
};
export default ContactApp;
Here is the explanation:
When you are calling the function to get the data from localstorage, you are also setting the contacts variable to the new data.
useEffect(() => {
const savedContacts = JSON.parse(localStorage.getItem("contacts"));
if (savedContacts) setContacts(savedContacts); // Here you are changing the value of 'contacts'
}, []);
BUT, You are also calling the localStorage.setItem method whenever the value of the contacts variable changes.
useEffect(() => {
localStorage.setItem("contacts", JSON.stringify(contacts));
}, [contacts]); // Here you are calling it when the contacts change.
So basically, when the component loads in the first useEffect. You are checking to see if contacts exist and setting the contacts variable to the existing contacts.
But you are also setting the value of the localStorage WHENEVER the value of the contacts variable changes.
its like:
Fetching Data the first time it loads and storing it --> because you have stored the data and the value of contacts has changed, it again sets the value of the contacts ----> which can lead to storing undefined or [] values if the contacts don't already have some default value.
Hope this helps.
Related
The object of this app is to allow input text and URLs to be saved to localStorage. It is working properly, however, there is a lot of repeat code.
For example, localStoredValues and URLStoredVAlues both getItem from localStorage. localStoredValues gets previous input values from localStorage whereas URLStoredVAlues gets previous URLs from localStorage.
updateLocalArray and updateURLArray use spread operator to iterate of previous values and store new values.
I would like to make the code more "DRY" and wanted suggestions.
/*global chrome*/
import {useState} from 'react';
import List from './components/List'
import { SaveBtn, DeleteBtn, DisplayBtn, TabBtn} from "./components/Buttons"
function App() {
const [myLeads, setMyLeads] = useState([]);
const [leadValue, setLeadValue] = useState({
inputVal: "",
});
//these items are used for the state of localStorage
const [display, setDisplay] = useState(false);
const localStoredValues = JSON.parse(
localStorage.getItem("localValue") || "[]"
)
let updateLocalArray = [...localStoredValues, leadValue.inputVal]
//this item is used for the state of localStorage for URLS
const URLStoredVAlues = JSON.parse(localStorage.getItem("URLValue") || "[]")
const tabBtn = () => {
chrome.tabs.query({ active: true, currentWindow: true }, function (tabs) {
const url = tabs[0].url;
setMyLeads((prev) => [...prev, url]);
// update state of localStorage
let updateURLArray = [...URLStoredVAlues, url];
localStorage.setItem("URLValue", JSON.stringify(updateURLArray));
});
setDisplay(false)
};
//handles change of input value
const handleChange = (event) => {
const { name, value } = event.target;
setLeadValue((prev) => {
return {
...prev,
[name]: value,
};
});
};
const saveBtn = () => {
setMyLeads((prev) => [...prev, leadValue.inputVal]);
setDisplay(false);
// update state of localStorage
localStorage.setItem("localValue", JSON.stringify(updateLocalArray))
};
const displayBtn = () => {
setDisplay(true);
};
const deleteBtn = () => {
window.localStorage.clear();
setMyLeads([]);
};
const listItem = myLeads.map((led) => {
return <List key={led} val={led} />;
});
//interates through localStorage items returns each as undordered list item
const displayLocalItems = localStoredValues.map((item) => {
return <List key={item} val={item} />;
});
const displayTabUrls = URLStoredVAlues.map((url) => {
return <List key={url} val={url} />;
});
return (
<main>
<input
name="inputVal"
value={leadValue.inputVal}
type="text"
onChange={handleChange}
required
/>
<SaveBtn saveBtn={saveBtn} />
<TabBtn tabBtn={tabBtn} />
<DisplayBtn displayBtn={displayBtn} />
<DeleteBtn deleteBtn={deleteBtn} />
<ul>{listItem}</ul>
{/* displays === true show localstorage items in unordered list
else hide localstorage items */}
{display && (
<ul>
{displayLocalItems}
{displayTabUrls}
</ul>
)}
</main>
);
}
export default App
Those keys could be declared as const and reused, instead of passing strings around:
const LOCAL_VALUE = "localValue";
const URL_VALUE = "URLValue";
You could create a utility function that retrieves from local storage, returns the default array if missing, and parses the JSON:
function getLocalValue(key) {
return JSON.parse(localStorage.getItem(key) || "[]")
};
And then would use it instead of repeating the logic when retrieving "localValue" and "URLValue":
const localStoredValues = getLocalValue(LOCAL_VALUE)
//this item is used for the state of localStorage for URLS
const URLStoredVAlues = getLocalValue(URL_VALUE)
Similarly, with the setter logic:
function setLocalValue(key, value) {
localStorage.setItem(key, JSON.stringify(value))
}
and then use it:
// update state of localStorage
let updateURLArray = [...URLStoredVAlues, url];
setLocalValue(URL_VALUE, updateURLArray);
// update state of localStorage
setLocalValue(LOCAL_VALUE, updateLocalArray)
The code below queries a record from an Atlassian Storage API.
with console.log(data) displays the records as objects objects.
with console.log(data.first_name) and console.log(data.last_name), I can successfully see the name Lucy and Carrots in the console.
Here is my Issue:
When I try to loop through the objects in other to display the records as per code below. it displays Error
TypeError: Cannot read property 'length' of undefined
at Object.App
If I remove the projects.length and try to display records, it will show error
TypeError: Cannot read property 'map' of undefined
Below is my effort so far
import api, { route } from "#forge/api";
import ForgeUI, { render, Fragment, Text, IssuePanel, useProductContext, useState, Component, useEffect} from "#forge/ui";
import { storage} from '#forge/api';
const fetchData = async () => {
//const data = {first_name: 'Lucy', last_name: 'Carrots' };
const data = await storage.get('key1');
console.log(data);
console.log(data.first_name);
console.log(data.last_name);
};
const App = () => {
const [ projects ] = useState(fetchData);
fetchData();
return (
<Fragment>
<Text> Display Objects Records</Text>
{projects.length ? projects.map((i, v) => (
<Text key={v}>
<Text>
<Text>First Name: {v.first_name}</Text>
<Text>Last Name: {v.last_name}</Text>
</Text></Text>
)): <Text>No data stored yet...</Text>}
</Fragment>
);
};
export const run = render(
<IssuePanel>
<App />
</IssuePanel>
);
I see the response data return an object, so you don't need to use array with map.
And you should call API in the useEffect.
const App = () => {
const [projects, setProjects] = useState(null);
useEffect(() => {
const fetchData = async () => {
const data = await storage.get("key1");
setProjects(data);
};
fetchData();
}, []);
...
{
projects ? (
<Text key={v}>
<Text>
<Text>First Name: {projects.first_name}</Text>
<Text>Last Name: {projects.last_name}</Text>
</Text>
</Text>
) : (
<Text>No data stored yet...</Text>
);
}
...
}
Try const [projects, setProjects] = useState([]) instead of const [projects] = useState(fetchData). This will make your state start out as an empty array that the API call can exchange for a filled one later by using setProjects().
Then, inside fetchProjects, you can call setProjects(data) to update your state, which will rerender your page.
Finally, calling fetchData() in the place you do now will cause it to be called every time your App is rendered, which is inefficient.
Instead, call it inside a useEffect() hook:
useEffect(fetchData, []);
This will call fetchData() once when the page is loaded.
I'm trying to navigate an array of orders stored in each "User". I am able to query and find ones that have orders but I'm not able to display them. I keep getting an error "Cannot read property 'map' of null". Where am I going wrong?
The image below shows how all the orders are stored in "order"
import React, { useState, useEffect } from "react";
import { Link } from "react-router-dom";
import { firestore } from "../../../FireBase/FireBase";
const OrdersAdmin = (props) => {
const [order, setOrder] = useState(null);
useEffect(() => {
const fetchOrder = async () => {
const doc = await firestore.collection("Users");
const snapshot = await doc.where("orders", "!=", []).get();
if (snapshot.empty) {
console.log("No matching documents.");
return <h1>No Orders</h1>;
}
var ans = [];
snapshot.forEach((doc) => {
console.log(doc.id, "=>", doc.data().orders);
setOrder(doc.data().orders)
});
};
fetchOrder();
}, [props]);
return (
<div className="adminOrders">
<h1>orders</h1>
{console.log(order)}
{order.map((orderItem) => (
<div className="singleOrder" key={orderItem.id}>
<p>{orderItem}</p>
</div>
))}
</div>
);
};
export default OrdersAdmin;
The issue is that the initial value of order is null. null does not have Array.prototype.map, therefore you get the error. Try updating your render to use conditional rendering to only attempt Array.prototype.map when order is truthy and an Array:
{order && order.length > 0 && order.map((orderItem) => (
<div className="singleOrder" key={orderItem.id}>
<p>{orderItem}</p>
</div>
))}
Otherwise you can use a better default value of an empty array for order which would have Array.prototype.map available to execute:
const [order, setOrder] = useState([]);
Hopefully that helps!
I am sending data from Node JS to React JS in array object. In React JS when I am setting response data I am getting error "Objects are not valid as a React child (found: object with keys {eventName, eventDate, merchantid}). If you meant to render a collection of children, use an array instead."
I checked one of the Stackoverflow post useState Array of Objects. I am also setting value same way, but I am getting error.
Below data I am sending from Node JS.
[
{
eventName: 'Sankranti',
eventDate: 2021-01-21T00:00:00.000Z,
merchantid: 'tp012345'
},
{
eventName: 'Sankranti 1',
eventDate: 2021-01-26T00:00:00.000Z,
merchantid: 'tp012345'
}
]
Below screen shot I can see error and response data on the console.
Below my code, I am getting error at setEventList(eventList => [...eventList, response]). Based on comments I added below code.
import React, { useState, useEffect } from 'react';
import { connect } from 'react-redux';
import Carousel from 'react-bootstrap/Carousel'
import axios from 'axios';
import DashboardNavBar from './DashboardNavBar';
import Header from './Header';
const DashboardPage = (props) => {
const [eventList, setEventList] = useState([])
const [index, setIndex] = useState()
if (!props.profileData) {
useEffect(() => {
(async () => {
const eventsList = await axios.get(
"http://localhost:3000/api/dashboard"
);
console.log(eventsList.data)
const response = eventsList.data
setEventList(eventList => [...eventList, response])
if(!response){
setErrorMsg('Please create Event and then add User !!')
}
})();
}, []);
}
const eventListRender = eventList.length > 0 ?
eventList.map((item,index) => {
console.log('item name: ', item[index].eventName)
return <Carousel.Item>{item[index].eventName}</Carousel.Item>
}) :
<Carousel.Item>No upcoming events</Carousel.Item>
const handleSelect = (selectedIndex) => {
console.log(eventList)
console.log(selectedIndex)
setIndex(selectedIndex)
}
return (
<div>
<DashboardNavBar />
<Header />
<p >Welcome !!!!!!</p>
<Carousel
activeIndex={index}
onSelect={handleSelect}
>
{eventListRender}
</Carousel>
</div>
);
}
const mapStateToProps = (state) => ({
profileData: state.auth.profileData
})
export default connect(mapStateToProps) (DashboardPage);
After adding below code it always reading first occurrence
const eventListRender = eventList.length > 0 ?
eventList.map((item,index) => {
console.log('item name: ', item[index].eventName)
return <Carousel.Item>{item[index].eventName}</Carousel.Item>
}) :
<Carousel.Item>No upcoming events</Carousel.Item>
Please find the updated results
Issue
Ok, your codesandbox confirms what I suspected. In your sandbox you've directly placed that mock response in your state as a flat array
const [eventList, setEventList] = useState([
{
eventName: "Sankranti",
eventDate: "2021-01-21T00:00:00.000Z",
merchantid: "tp012345"
},
{
eventName: "Sankranti 1",
eventDate: "2021-01-26T00:00:00.000Z",
merchantid: "tp012345"
}
]);
This allows the render to work as you expected, simply mapping over this flat array of objects.
eventList.map((item, index) => {
return <Carousel.Item>{item.eventName}</Carousel.Item>;
})
But in your original code you are not updating your state to be a flat array. The response is an array, i.e. [object1, object2] and you append this array to the end of your state's eventList array.
setEventList(eventList => [...eventList, response])
This updates your state to something like this [[object1, object2]], so the mapping function you used only maps one element.
eventList.map((item, index) => {
return <Carousel.Item>{item[index].eventName}</Carousel.Item>;
})
The reason is because you used the array index of the outer (recall eventList is an array of length 1) to access into the inner nested array (array of length 2). In iterating the outer array the index only reaches value 0, so only the zeroth element of the inner array is rendered.
See a more accurate reproduction of your issue in this code:
const response = [
{
eventName: "Sankranti",
eventDate: "2021-01-21T00:00:00.000Z",
merchantid: "tp012345"
},
{
eventName: "Sankranti 1",
eventDate: "2021-01-26T00:00:00.000Z",
merchantid: "tp012345"
}
];
function App() {
const [eventList, setEventList] = useState([]);
useEffect(() => {
setEventList((eventList) => [...eventList, response]);
}, []);
const eventListRender =
eventList.length > 0 ? (
eventList.map((item, index) => {
return <Carousel.Item>{item[index].eventName}</Carousel.Item>;
})
) : (
<Carousel.Item>No upcoming events</Carousel.Item>
);
return (
<div className="App">
<h1>Hello CodeSandbox</h1>
<h2>Start editing to see some magic happen!</h2>
<Carousel>{eventListRender}</Carousel>
</div>
);
}
Solution
If the response data is also an array then it seems you should spread it into your eventList state array so it remains a nice, flat array.
Additionally, as pointed out by #Ashish, your useEffect hook usage is invalid and breaks the rules of hooks by being placed in a conditional block. The effect needs to be in the body of the component, so the condition should be tested in the effect callback. Refactor the anonymous async function to be a standard named function, and invoke in a conditional check within the effect callback.
useEffect(() => {
const getEvents = async () => {
const eventsList = await axios.get("http://localhost:3000/api/dashboard");
console.log(eventsList.data);
const response = eventsList.data;
setEventList((eventList) => [
...eventList, // <-- copy previous state
...response, // <-- spread array response
]);
if (!response) {
setErrorMsg("Please create Event and then add User !!");
}
};
if (!props.profileData) { // <-- check condition for fetching data
getEvents();
}
}, []);
const eventListRender =
eventList.length > 0 ? (
eventList.map((item, index) => {
return <Carousel.Item key={index}>{item.eventName}</Carousel.Item>;
})
) : (
<Carousel.Item>No upcoming events</Carousel.Item>
);
Demo with mocked axios data fetch.
i want to pass the string from asyncstorage to a state variable using hooks, but it doesn't work, trying for hours but still doesn't work.
here is the code:
const [cartitems, cartitemsfunc] = useState('');
const d = async () => {
let items = await AsyncStorage.getItem('items');
console.log('items from cart:' + items);
cartitemsfunc(items);
console.log('items from cart2:' + cartitems);
};
d();
when i try console logging cartitems it logs an empty string in the console,but items logs out the string
can someone please tell me where i went wrong
thanks in advance!!!
As mentioned in the comments and link supplied, useState is asynchronous so setting a value and immediately reading it in the following line will not yield consistent result:
cartitemsfunc(items); // async call
console.log('items from cart2:' + cartitems); // cartitems not updated yet
It is important to also understand that whenever you update state using useState, the component will render again. If you have a method call in the body of the app it will be run everytime you update state. So what you have is a scenario where you are making a call to update state, but the method is being executed and ends up overwriting your changes.
const d = async () => {
let items = await AsyncStorage.getItem('items');
console.log('items from cart:' + items);
cartitemsfunc(items);
console.log('items from cart2:' + cartitems);
};
d(); // this will run every time the component renders - after you update state
If you only need the value at initial render, then call the method from useEffect and set the dependency chain to [] so it only runs once at first render, and not every time state is updated.
Below is an example that demonstrates getting/setting values from localStorage and also updating the state directly.
CodeSandbox Demo
import React, { useState, useEffect } from "react";
import AsyncStorage from "#react-native-community/async-storage";
import "./styles.css";
export default function App() {
const [cartItems, setCartItems] = useState(null);
const setLSItems = async () => {
await AsyncStorage.setItem(
"items",
JSON.stringify([{ id: "foo", quantity: 1 }, { id: "bar", quantity: 2 }])
);
getLSItems(); // or setCartItems("Foo");
};
const clearLSItems = async () => {
await AsyncStorage.removeItem("items");
getLSItems(); // or or setCartItems(null);
};
const getLSItems = async () => {
const items = await AsyncStorage.getItem("items");
setCartItems(JSON.parse(items));
};
// bypass using local storage
const setCartItemsDirectly = () => {
setCartItems([{ id: "baz", quantity: 3 }]);
};
useEffect(() => {
getLSItems();
}, []); // run once at start
return (
<div className="App">
<div>
<button onClick={setLSItems}>Set LS Items</button>
<button onClick={clearLSItems}>Clear LS Items</button>
</div>
<div>
<button onClick={setCartItemsDirectly}>Set Cart Items Directly</button>
</div>
<hr />
{cartItems &&
cartItems.map((item, index) => (
<div key={index}>
item: {item.id} | quantity: {item.quantity}
</div>
))}
</div>
);
}
Since setState is async you will need to observe when it finishes, this can be easily done using useEffect and adding caritems to the dependencies array
const [cartitems, cartitemsfunc] = useState('');
const d = async () => {
let items = await AsyncStorage.getItem('items');
console.log('items from cart:' + items);
cartitemsfunc(items);
};
useEffect(()=> {
console.log('items from cart2:' + cartitems);
}, [caritems]);
d();
I think here console.log() statement is executed before updating the state. As here await has been used so it will execute the next lines before getting the result.
Therefore , in this type of situation we use combination of useEffect() and useState(). useEffect() for getting the data and useState() for updating the state and re-render the UI.