Memorize fetched results in component - reactjs

I'm working on a component that adds images to items. You can either upload your own image or pick an image, loaded from an API based on the name of the item.
Here is the root component:
const AddMedia = (props) => {
const [currentTab, setCurrentTab] = useState(0);
const [itemName, setItemName] = useState(props.itemName);
return (
<div>
<Tabs
value={currentTab}
onChange={() => setCurrentTab(currentTab === 0 ? 1 : 0)}
/>
<div hidden={currentTab !== 0}>
<FileUpload />
</div>
<div hidden={currentTab !== 1}>
{currentTab === 1 && <ImagePicker searchTerm={itemName} />}
</div>
</div>
);
};
And here is the <ImagePicker />:
import React, { useState, useEffect } from "react";
function ImagePicker({ searchTerm, ...props }) {
const [photos, setPhotos] = useState([]);
const searchForImages = async (keyword) => {
const images = await api.GetImagesByKeyword(keyword);
return images;
};
useEffect(() => {
const result = searchForImages(searchTerm);
setPhotos(result);
}, []);
return (
<>
{photos.map(({ urls: { small } }, j) => (
<img alt={j} src={small} className={classes.img} />
))}
</>
);
}
const areSearchTermsEqual = (prev, next) => {
return prev.searchTerm === next.searchTerm;
};
const MemorizedImagePicker = React.memo(ImagePicker, areSearchTermsEqual);
export default MemorizedImagePicker;
What I'm struggling with is getting the component to not fetch the results again if the searchTerm hasn't changed. For example, when the component loads it's on tab 0 (upload image), you switch to tab 1 (pick an image) and it fetches the results for searchTerm, then you switch to 0 and again to 1 and it fetches them again, although the searchTerm hasn't changed. As you can see, I tried using React.memo but to no avail. Also, I added the currentTab === 1 to stop it from fetching the photos when the root component renders and fetch them only if the active tab is 1.

You should add the searchTerm as dependency of the useEffect so that it will not fetch again if searchTerm hasn't change:
useEffect(() => {
const result = searchForImages(searchTerm);
setPhotos(result);
}, [searchTerm]);
Additional information, if you are using eslint to lint your code, you can use the react-hooks/exhaustive-deps rule to avoid this kind of mistake.

Related

React Context. how to avoid "Cannot read properties of undefined" error before having a value

I am learning React, and trying to build a photo Album with a a modal slider displaying the image clicked (on a different component) in the first place.
To get that, I set <img src={albums[slideIndex].url} /> dynamically and set slideIndex with the idof the imgclicked , so the first image displayed in the modal slider is the one I clicked.
The problem is that before I click in any image albums[slideIndex].urlis obviously undefined and I get a TypeError :cannot read properties of undefined
How could I solve that?
I tried with data checks with ternary operator, like albums ? albums[slideIndex].url : "no data", but doesn't solve it.
Any Ideas? what i am missing?
this is the component where I have the issue:
import React, { useContext, useEffect, useState } from "react";
import { AlbumContext } from "../../context/AlbumContext";
import AlbumImage from "../albumImage/AlbumImage";
import "./album.css";
import BtnSlider from "../carousel/BtnSlider";
function Album() {
const { albums, getData, modal, setModal, clickedImg } =
useContext(AlbumContext);
console.log("clickedImg id >>", clickedImg.id);
useEffect(() => {
getData(); //-> triggers fetch function on render
}, []);
///////////
//* Slider Controls
///////////
const [slideIndex, setSlideIndex] = useState(clickedImg.id);
console.log("SlideINDEx", slideIndex ? slideIndex : "no hay");
const nextSlide = () => {
if (slideIndex !== albums.length) {
setSlideIndex(slideIndex + 1);
} else if (slideIndex === albums.length) {
setSlideIndex(1);
}
console.log("nextSlide");
};
const prevSlide = () => {
console.log("PrevSlide");
};
const handleOnclick = () => {
setModal(false);
console.log(modal);
};
return (
<div className="Album_Wrapper">
<div className={modal ? "modal open" : "modal"}>
<div>
<img src={albums[slideIndex].url} alt="" />
<button className="carousel-close-btn" onClick={handleOnclick}>
close modal
</button>
<BtnSlider moveSlide={nextSlide} direction={"next"} />
<BtnSlider moveSlide={prevSlide} direction={"prev"} />
</div>
</div>
<div className="Album_GridContainer">
{albums &&
albums.map((item, index) => {
return (
<AlbumImage
className="Album_gridImage"
key={index}
image={item}
/>
);
})}
</div>
</div>
);
}
export default Album;
THis is my AlbumContext :
import React, { createContext, useState } from "react";
export const AlbumContext = createContext();
export const AlbumContextProvider = ({ children }) => {
const [albums, setAlbums] = useState();
const [modal, setModal] = useState(false);
const [clickedImg, setClickedImg] = useState("");
const showImg = (img) => {
setClickedImg(img);
setModal(true);
console.log(clickedImg);
};
const getData = async () => {
try {
const response = await fetch(
"https://jsonplaceholder.typicode.com/albums/1/photos"
);
const obj = await response.json();
console.log(obj);
setAlbums(obj);
} catch (error) {
// console.log(error.response.data.error);
console.log(error);
}
};
console.log(`Albums >>>`, albums);
return (
<AlbumContext.Provider
value={{ albums, getData, showImg, modal, setModal, clickedImg }}
>
{children}
</AlbumContext.Provider>
);
};
Thanks very much in advance
Your clickedImg starts out as the empty string:
const [clickedImg, setClickedImg] = useState("");
And in the consumer, you do:
const [slideIndex, setSlideIndex] = useState(clickedImg.id);
So, it takes the value of clickedImg.id on the first render - which is undefined, because strings don't have such properties. As a result, both before and after fetching, slideIndex is undefined, so after fetching:
albums ? albums[slideIndex].url : "no data"
will evaluate to
albums[undefined].url
But albums[undefined] doesn't exist, of course.
You need to figure out what slide index you want to be in state when the fetching finishes - perhaps start it at 0?
const [slideIndex, setSlideIndex] = useState(0);
maybe because your code for checking albums is empty or not is wrong and its always return true condition so change your code to this:
<div className="Album_GridContainer">
{albums.length > 0 &&
albums.map((item, index) => {
return (
<AlbumImage
className="Album_gridImage"
key={index}
image={item}
/>
);
})}
</div>
change albums to albums.length

Increment a part of URL when a button is clicked in ReactJS

I am creating a web app, which is basically an image gallery for a browser game.
The avatars are stored in the game in this format:
https://websitelink.com/avatar/1
https://websitelink.com/avatar/2
https://websitelink.com/avatar/3
So i want to build 2 navigation buttons, one will increment the counter, to move to next image and another one will decrement the counter to move to previous image.
I tried to use props, but since props are immutable it didn't work.
How do I approach building this web app?
Here is the minimal code which may help you to understand about the React Component, props and state.
// parent compoment
import { useState } from "react"
export const GameImageGallery = () => {
const [num, setNum] = useState(0)
const increaseDecrease = (state) => {
if (state === "+") {
setNum(num + 1)
}
if (state === "-") {
setNum(num - 1)
}
}
return (
<>
<button onClick={() => increaseDecrease("-")}>--</button>
<button onClick={() => increaseDecrease("+")}>++</button>
<Image url={`https://websitelink.com/avatar/${num}`} />
</>
)
}
// child component to show image
const Image = ({ url }) => {
return <img src={url} alt="image" />
}
you can do this thing,
const [id,setId]=useState(0);
useEffect(() => {
},[id])
const increment = () => {
setId(id++);
}
const decrement = () => {
setId(id--);
}
return(
<button onClick={increment}>Add</button>
<button onClick={decrement}>remove</button>
<img url={`https://websitelink.com/avatar/${id}`} />
)
useRef is ideal to manage data persistently in a component.
Example:
import { useRef } from 'react'
...
const App = () => {
const links = useRef({url1Ctr : 1})
const onBtnClick = () => {
links.current = { url1Ctr: links.current.url1Ctr + 1}
}
...
}

Rerender component after function in provider ends

I'm trying to set components with 3 functionalities. Displaying PokemonList, getting random pokemon and find one by filters. Getting random pokemon works great but since 2 days I'm trying to figure out how to set pokemon list feature correctly
Below full code from this component.
It's render when click PokemonsList button inside separate navigation component and fire handleGetPokemonList function in provider using context.
The problem is that I can't manage rerender components when PokemonList is ready. For now i need to additionally fire forceUpadte() function manually (button onClick = () => forceUpdate())
I tried to use useEffect() in PokemonList component but it didn't work in any way.
I was also sure that after fetching data with fetchData() function I can do .then(changeState of loading) but it didn't work also.
What Am I missing to automatically render data from fetch in provider in PokemonList component? I'm receiving error about no data exist but if I use forceUpdate then everything is ok
Complete repo here: https://github.com/Mankowski92/poke-trainer
handleGetPokemonList function in provider below
const handleGetPokemonList = () => {
setCurrentPokedexOption('pokemonList');
async function fetchData() {
setImgLoaded(false);
let res = await fetch(`${API}?offset=0&limit=6/`);
let response = await res.json();
response.results.forEach((item) => {
const fetchDeeper = async () => {
let res = await fetch(`${item.url}`);
let response = await res.json();
let eachPoke = {
id: response.id,
name: response.name,
artwork: response.sprites.other['officialartwork'].front_default,
stats: response.stats,
};
fetchedPokemons.push(eachPoke);
};
fetchDeeper();
});
setPokemonList(fetchedPokemons);
if (fetchedPokemons) {
return setLoading(false);
}
}
fetchData()
.then((res) => setLoading(res))
.catch((err) => console.log('error', err));
};
PokemonList component below
import React, { useContext, useState, useCallback } from 'react';
import { StyledPokemonListContainer } from './PokemonList.styles';
import { PokemonsContext } from '../../../providers/PokemonsProvider';
const PokemonList = () => {
const ctx = useContext(PokemonsContext);
const [, updateState] = useState();
const forceUpdate = useCallback(() => updateState({}), []);
const { handleSetImgLoaded } = useContext(PokemonsContext);
return (
<>
{ctx.currentPokedexOption === 'pokemonList' ? (
<StyledPokemonListContainer>
{ctx.pokemonList && ctx.pokemonList.length ? (
ctx.pokemonList.map((item, i) => (
<div className="each-pokemon-container" key={i}>
<div className="poke-id">{item.id}</div>
<div className="poke-name">{item.name}</div>
<img className="poke-photo" onLoad={() => handleSetImgLoaded()} src={item ? item.artwork : ''} alt="" />
</div>
))
) : (
<div className="render-info">Hit rerender button</div>
)}
{/* {ctx.pokemonList ? <div>{ctx.pokemonList[0].name}</div> : <div>DUPPSKO</div>} */}
<div className="buttons">
<button onClick={() => console.log('PREVOIUS')}>Previous</button>
<button className="rerender-button" onClick={() => forceUpdate()}>
RERENDER
</button>
<button onClick={() => console.log('NEXT')}>Next</button>
</div>
</StyledPokemonListContainer>
) : null}
</>
);
};
export default PokemonList;

Need useEffect hook invoke when URL changes

I am trying to have this component load data depending on its current url whether /global or /my-posts. The useEffect() grabs the data from the first loading of the component but when i change to another url i expected useEffect to check the url again and load the correct data but instead i'm stuck with the data from the first load. How do i get useEffect to invoke every time i click between different urls like /global and /my-posts url.
export default function Dashboard() {
const [allRecipes, setAllRecipes] = useState([]);
const [myRecipes, setMyRecipes] = useState([]);
const currentUrl = window.location.pathname;
useEffect(() => {
if (currentUrl === '/dashboard/global') {
console.log('hello');
trackPromise(
RecipeService.getAllRecipes()
.then((data) => {
setAllRecipes(data);
}),
);
} else if (currentUrl === '/dashboard/my-posts') {
console.log('hi');
trackPromise(
RecipeService.getRecipes()
.then((data) => {
setMyRecipes(data);
}),
);
}
}, []);
console.log(window.location.pathname);
return (
<>
<div className="dashboard">
<DashboardHeader />
<div className="created-posts">
{allRecipes.length !== 0
? allRecipes.map((recipe) => <Post recipe={recipe} key={uuidv1()} />)
: null}
{myRecipes.length !== 0
? myRecipes.recipes.map((recipe) => <Post recipe={recipe} key={uuidv1()} />)
: null}
{currentUrl === '/dashboard/create' ? <CreateForm /> : null}
<LoadingIndicator />
</div>
</div>
</>
);
}
to make React.useEffect run on every currentUrl change, you have to add it to useEffect dependencies array.
// first we need to control the state of window.location.pathname by react not the browser
// and make react state be the only source of truth.
const pathname = window.location.pathname
// manage currentUrl in state.
const [currentUrl, setCurrentUrl] = React.useState(pathname)
React.useEffect(() => {
setCurrentUrl(pathname)
}, [pathname])
// now you would add the contolled `currentUrl` state to its useEffect deps.
useEffect(() => {
if (currentUrl === '/dashboard/global') {
// ..........
} else if (currentUrl === '/dashboard/my-posts') {
// ..........
}
}, [currentUrl]);

React: Passing up data from child component into parent does not update values in parent

// Edit --
This may help:
Project Hatchways
Link to issue -
Issue
As the codes stands right now, the results from the tags still aren't rendering results.
I have a component App.js that renders some children. One of them is 2 search bars. The second search bar TagSearch is supposed to render results from tag creation. What I'm trying to do is pass data from Student where the tags live, and pass them up to the App component in order to inject them into my Fuse instance in order for them to be searched. I have tried to create a function update in App.js and then pass it down to Student.js in order for the tags to update in the parent when a user searches the tags. For some reason, I'm getting a TypeError that states update is not a function.
I put in console logs to track where the tags appear. The tags appear perfectly fine in Student.js, but when I console log them in App.js, the tags just appear as an empty array which tells me they aren't being properly passed up the component tree from Student.js to App.js.
// App.js
import axios from "axios";
import Fuse from "fuse.js";
import Student from "./components/Student";
import Search from "./components/Search";
import TagSearch from "./components/TagSearch";
import "./App.css";
function App() {
const [loading, setLoading] = useState(true);
const [students, setStudents] = useState([]);
const [query, updateQuery] = useState("");
const [tags, setTags] = useState([]);
const [tagQuery, setTagQuery] = useState("");
console.log("tags from app: ", tags);
const getStudents = async () => {
setLoading(true);
try {
const url = `private url for assignment`;
const response = await axios.get(url);
setStudents(response.data.students);
setLoading(false);
} catch (err) {
console.log("Error: ", err);
}
};
const fuse = new Fuse(students, {
keys: ["firstName", "lastName"],
includeMatches: true,
minMatchCharLength: 2,
});
const tagFuse = new Fuse(tags, {
keys: ["text", "id"],
includesMatches: true,
minMatchCharLength: 2,
});
function handleChange(e) {
updateQuery(e.target.value);
}
function handleTags(e) {
setTagQuery(e.target.value);
}
const results = fuse.search(query);
const studentResults = query ? results.map((s) => s.item) : students;
const tagResults = tagFuse.search(tagQuery);
const taggedResults = tagQuery ? tagResults.map((s) => s.item) : tags;
const update = (t) => {
t = tags; // changed this to make sure t is tags from this component's state
setTags(t);
};
useEffect(() => {
getStudents();
}, []);
if (loading) return "Loading ...";
return (
<div className="App">
<main>
<Search query={query} handleChange={handleChange} />
<TagSearch query={tagQuery} handleTags={handleTags} />
{studentResults &&
studentResults.map((s, key) => <Student key={key} students={s} update={update} />)}
{taggedResults &&
taggedResults.map((s, key) => (
<Student key={key} students={s} update={update} />
))}
</main>
</div>
);
}
export default App;
// Student.js
import Collapsible from "../components/Collapsible";
import findAverage from "../helpers/findAverage";
import Styles from "../styles/StudentStyles";
const KeyCodes = {
comma: 188,
enter: 13,
};
const delimiters = [KeyCodes.comma, KeyCodes.enter];
const Student = ({ students, update }) => {
const [isOpened, setIsOpened] = useState(false);
const [tags, setTags] = useState([]);
const collapse = () => {
setIsOpened(!isOpened);
};
const handleDelete = (i) => {
const deleted = tags.filter((tag, index) => index !== i);
setTags(deleted);
};
const handleAddition = (tag, i) => {
setTags([...tags, tag]);
};
useEffect(() => {
update(tags);
}, []);
return (
<Styles>
<div className="student-container">
<img src={students.pic} alt={students.firstName} />
<div className="student-details">
<h1>
{students.firstName} {students.lastName}
</h1>
<p>Email: {students.email}</p>
<p>Company: {students.company}</p>
<p>Skill: {students.skill}</p>
<p>Average: {findAverage(students.grades)}</p>
<Collapsible
students={students}
delimiters={delimiters}
handleDelete={handleDelete}
handleAddition={handleAddition}
isOpened={isOpened}
tags={tags}
/>
</div>
</div>
<button onClick={collapse}>+</button>
</Styles>
);
};
export default Student;
Ciao, try to call update function every time you update tags in Student. Something like this:
const handleDelete = (i) => {
const deleted = tags.filter((tag, index) => index !== i);
setTags(deleted);
update(deleted);
};
const handleAddition = (tag, i) => {
let result = tags;
result.push(tag);
setTags(result);
update(result);
};
In this way, every time you change tags in Student, you will update App state.
An alternative could be use useEffect deps list. In Student, modify useEffect like this:
useEffect(() => {
update(tags);
}, [tags]);
This means that, every time tags will update, useEffect will be triggered and update function will be called.

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