I have written the following codes but the console prompts an error that says 'this.state.result.map is not a function' (in the 'return'). Just wondering if anyone has any idea what is wrong. Thanks!
class App extends React.Component {
constructor (props) {
super(props);
this.state = {
result: []
}
}
componentDidMount(){
const fetchGithub = (loginName) =>
fetch(`https://api.github.com/users/${loginName}/followers`)
.then(response => response.json());
const processJson= () =>
fetchGithub('ericelliott')
.then(json => {
const userList = json.map(user =>
user.login
)
const result = userList.join(', ')
this.setState({result: result})
});
processJson();
}
render(){
return (
<div>
{this.state.result.map(user => (
<div>
<div>
{user.login}
</div>
</div>
))}
</div>
)
}
}
JS map is reserved for Arrays, as you are using const result = userList.join(', '). This turns your result array to a string therefore map function is no longer available. Just remove that line.
Related
Learning react
Trying to loop through an object from an API call that returns a json object and display it but struggling to implement it
This is the component that should render it
export default class ProfilePage extends Component {
constructor() {
super();
this.state = { data: '' };
}
mapObject(object, callback) {
return Object.keys(object).map(function (key) {
return callback(key, object[key]);
})
}
async componentDidMount() {
const response = await fetch(`https://indapi.kumba.io/webdev/assignment`);
const json = await response.json();
// console.log(json)
this.setState({ data: json });
}
render() {
const data = this.state.data
console.log(data)
return (
<div className="row">
{Object.values(data).map(data => {
<div key={key}>
{data[key]}
</div>
})
}
Woerkkk please
</div>
);
}
}
All I'm getting is a blank screen.
in the console i get the error 'key' is not defined no-undef
You are missing a return statement in your map for your render method.
Edit: Key is not returned from Object.values
Either reconfigure with a return statement like so:
{Object.keys(data).map(key => {
return (<div key={key}>
{data[key]}
</div>);
})
Or alternatively you can implicitly return from arrow function using brackets
{Object.keys(data).map(key => (
<div key={key}>
{data[key]}
</div>)
))
Using Object.values(myObj) you can get all object values as a array. So, with this array, you can iterate over the array and show your items, like this:
{Object.values(myObj).map(value => <p>{value}</p>)}
Don't forget use key prop when iterating.
You can use useState and useEffect to fetch the object data
const App = () => {
const [objData, setObjData] = useState({});
const [objItems, setObjItems] = useState([]);
const fetchObj = async () => {
const response = await fetch(`https://indapi.kumba.io/webdev/assignment`);
const data = await response.json();
setObjData(data);
setObjItems(data.items);
}
useEffect(() => {
fetchObj()
},[]);
return(
<div>
<h1> Order Id :{objData.order_id}</h1>
// or any other objData keys
<h1>Items : </h1>
<ul>
{
objItems.map((i, idx) => {
return(
<li key={idx}>Name : {i.name} , Category: {i.category}, Price: {i.price}, Currency: {i.currency}</li>
)
})
}
</ul>
</div>
)
}
export default App;
I made a classical component and a functional component, they should both do the same thing.
They both pull data from my API and then should map it to a Div. However, this doesn't work with the functional component and I'd rather use a functional component with hooks.
I've also tried using the "UseLayoutEffect" hook. I know this is happening because the first time the component loads, Games is undefined and it tries to map undefined, but after a tiny delay the API call is finished and Games is now an array of objects. However, it already tried to map undefined. I have a condition 'Games' which should stop it from being mapped if its undefined, but for some reason it passes this condition.
Classical component (working):
class Player extends React.Component {
constructor(props) {
super(props);
this.state = {
games: [],
players: {},
};
}
componentDidMount() {
this.fetchData()
}
async fetchData() {
const id = window.location.pathname.split('/')[2];
const games = await axios(`/api/players/${id}`);
this.setState({ games: games.data });
}
render() {
return(
<div>
{this.state.games.map((game, i) => (
<div className="historyId" key={i}>{game.match_id}</div>
))}
</div>
);
}
}
Functional component (not-working):
Uncaught TypeError: Cannot read property 'map' of undefined
at Player (bundle.js:1422)
const Player = (props) => {
let { id } = useParams();
const [games, setGames] = useState({});
useEffect(() => {
async function fetchData() {
const response = await axios(`/api/players/${id}`);
setGames(response);
}
fetchData();
}, []);
return (
<div className="historyContainer">
<h1>Match history here...</h1>
{games && games.data.map((game, i) => <div>{game.match_id}</div>)}
</div>
);
}
You're checking if games exists but it has a default value (empty object) so it will always exist. You're not checking if games.data exists - it won't until your HTTP request is completed.
Try this instead:
{games.data && games.data.map((game, i) => <div>{game.match_id}</div>)}
Try this:
const Player = (props) => {
let { id } = useParams();
const [games, setGames] = useState([]);
useEffect(() => {
async function fetchData() {
const {data} = await axios(`/api/players/${id}`);
setGames(data);
}
fetchData();
}, []);
return (
<div className="historyContainer">
<h1>Match history here...</h1>
{games.map((game, i) => <div>{game.match_id}</div>)}
</div>
);
}
this works for me:
const {products}=useContext(ProductContext);
const [product, setProduct]=useState();
const getProduct=()=>{
if(props.match.params.id){
const res=products;
const data= res.filter(p=>{
return p.id === props.match.params.id;
})
setProduct(data);
}
}
useEffect(() => {
getProduct()
},[])
return (
<div>
{product && product.map(items=>(
<div key={items.id}>
<h2>{items.name}</h2>
</div>
))}
</div>
)
}
I'm making two calls from an API. I want to display the top results for airing shows and top tv shows. I have all of the data being returned from both API calls, but my code isn't efficient. I'd like to somehow take my returned data and display it in a single component (TopAnime) that will then map and return the information provided.
I figured reduce would be the best route, but I'm fumbling at this point. My thought process was to reduce the returned data from the API into an array. Take that reduced array and pass it as my new state and then have my component display it without having to write duplicate code. Both topTv and topAIring are showing because I've written the component twice, but it's clearly not best practice to repeat code.
class HomePage extends Component {
state = {
topTv: [],
topAiring: []
}
async getData() {
const api = "https://api.jikan.moe/v3"
const urls = [
`${api}/top/anime/1/tv`,
`${api}/top/anime/1/airing`
];
return Promise.all(
urls.map(async url => {
return await fetch(url) // fetch data from urls
})
)
.then(responses => // convert response to json and setState to retrieved data
Promise.all(responses.map(resp => resp.json())).then(data => {
console.log("data", data)
// const results = [...data[0].top, ...data[1].top]; // data from TV & data from airing
const reduceResults = data.reduce((acc, anime) => {
return acc + anime
}, [])
console.log('reduce', reduceResults);
const tvResults = data[0].top // data from TV
const airingResults = data[1].top // data from airing
this.setState({
topTv: tvResults,
topAiring: airingResults
});
})
)
.catch(err => console.log("There was an error:" + err))
}
componentDidMount() {
this.getData();
}
render() {
return (
<HomeWrapper>
<h2>Top anime</h2>
<TopAnime>
{this.state.topTv.map((ani) => {
return (
<div key={ani.mal_id}>
<img src={ani.image_url} alt='anime poster' />
<h3>{ani.title}</h3>
</div>
)
}).splice(0, 6)}
</TopAnime>
<h2>Top Airing</h2>
<TopAnime>
{this.state.topAiring.map((ani) => {
return (
<div key={ani.mal_id}>
<img src={ani.image_url} alt='anime poster' />
<h3>{ani.title}</h3>
</div>
)
}).splice(0, 6)}
</TopAnime>
</HomeWrapper>
)
}
}
Since the response from API contains a flag called rank you can use the Array.prototype.filter to only show shows ranked 1-6.
Working demo here
import React, { Component } from "react";
import { TopAnime } from "./TopAnime";
export class HomePage extends Component {
state = {
topTv: [],
topAiring: []
};
async getData() {
const api = "https://api.jikan.moe/v3";
const urls = [`${api}/top/anime/1/tv`, `${api}/top/anime/1/airing`];
return Promise.all(
urls.map(async url => {
return await fetch(url); // fetch data from urls
})
)
.then((
responses // convert response to json and setState to retrieved data
) =>
Promise.all(responses.map(resp => resp.json())).then(data => {
// if you care about mutation use this
const topTvFiltered = data[0].top.filter( (item) => item.rank <= 6 );
const topAiringFiltered = data[1].top.filter( (item) => item.rank <= 6 );
this.setState({
topTv: topTvFiltered,
topAiring: topAiringFiltered
});
})
)
.catch(err => console.log("There was an error:" + err));
}
componentDidMount() {
this.getData();
}
render() {
const { topTv, topAiring } = this.state;
return (
<React.Fragment>
{ topTv.length > 0 ? <h2>Top TV</h2> : null }
{this.state.topTv.map((item, index) => (
<TopAnime key={index} title={item.title} image={item.image_url} />
))}
{ topAiring.length > 0 ? <h2>Top airing</h2> : null }
{this.state.topAiring.map((item, index) => (
<TopAnime key={index} title={item.title} image={item.image_url} />
))}
</React.Fragment>
);
}
}
I'm making an application where I have to grab certain data from the Github API. I need to grab the name, url, language and latest tag. Because the latest tag is in a separate url, I need to make another fetch call there to grab that data.
I'm running into a certain amount of errors.
1st being the typeError cannot read property 'name' of undefined. I'm sure this is from the fetch call to the tag url where there isn't any data. I'm not really sure how to check if it's undefined. I've tried calling checking to see if the typeof data is undefined and so on but still get the error.
2nd problem being my tag url data doesn't show up with the other data. I'm sure I'm chaining the data wrong because when I click the add button it shows up.
Here is my code:
import React, { Component } from 'react'
import './App.css'
class App extends Component {
state = {
searchTerm: '',
repos: [],
favourites: []
}
handleChange = e => {
const { searchTerm } = this.state
this.setState({ searchTerm: e.target.value })
if (searchTerm.split('').length - 1 === 0) {
this.setState({ repos: [] })
}
}
findRepos = () => {
const { searchTerm } = this.state
// First api call here
fetch(`https://api.github.com/search/repositories?q=${searchTerm}&per_page=10&access_token=${process.env.REACT_APP_TOKEN}
`)
.then(res => res.json())
.then(data => {
const repos = data.items.map(item => {
const { id, full_name, html_url, language } = item
const obj = {
id,
full_name,
html_url,
language,
isFavourite: false
}
// Second api call here. I need the data from map to get the tags for the correct repo
fetch(`https://api.github.com/repos/${full_name}/tags`)
.then(res => res.json())
.then(data => {
obj.latest_tag = data[0].name
})
.catch(err => console.log(err))
return obj
})
this.setState({ repos })
})
.catch(err => console.log(err))
}
render() {
const { searchTerm, repos, favourites } = this.state
return (
<div className="App">
<h1>My Github Favorites</h1>
<input
type="text"
placeholder="search for a repo..."
value={searchTerm}
onChange={e => this.handleChange(e)}
onKeyPress={e => e.key === 'Enter' && this.findRepos()}
/>
<button
type="submit"
onClick={this.findRepos}>
Search
</button>
<div className="category-container">
<div className="labels">
<h5>Name</h5>
<h5>Language</h5>
<h5>Latest Tag</h5>
</div>
// Here I list the data
{repos.map(repo => (
<div key={repo.id}>
<a href={repo.html_url}>{repo.full_name}</a>
<p>{repo.language}</p>
{repo.latest_tag ? <p>{repo.latest_tag}</p> : <p>-</p>}
<button onClick={() => this.addToFavs(repo)}>Add</button>
</div>
))}
<h1>Favourites</h1>
{favourites.map(repo => (
<div key={repo.id}>
<a href={repo.html_url}>{repo.full_name}</a>
<p>{repo.language}</p>
<p>{repo.latest_tag}</p>
<button>Remove</button>
</div>
))}
</div>
</div>
)
}
}
export default App
If you use Promise.all(), you could rewrite your code like the following.
findRepos = () => {
const { searchTerm } = this.state;
// First api call here
const first = fetch(
`https://api.github.com/search/repositories?q=${searchTerm}&per_page=10&access_token=${
process.env.REACT_APP_TOKEN
}`
);
// Second api call here. I need the data from map to get the tags for the correct repo
const second = fetch(`https://api.github.com/repos/${full_name}/tags`);
Promise.all([first, second])
.then((res) => Promise.all(res.map(r => r.json())))
.then([data1, data2] => {
data1.then((firstData) => {
/*Do something you want for first.*/
});
data2.then((secondData) => {
/*Do something you want for second.*/
});
})
.catch((err) => console.log(err));
};
Hope this works for you.
I'm trying to learn React and I'm a beginner when it comes to Javascript. Right now I'm working on an app that is fetching data from Flickr's API. The problem is that when I try to use the map method on the props in the Main.js component I get an error saying "Uncaught TypeError: this.props.photos.map is not a function". After searching here on Stackoverflow I think the problem is that this.props are javascript objects and not an array. The problem is that I can't figure out how to make it an array. Can anyone explain what I'm doing wrong?
My code:
class App extends Component {
constructor() {
super();
this.state = {
}
}
componentDidMount() {
let apiKey = 'xxxxxxxxxxxxxxxxxx';
let searchKeyword = 'nature';
let url = `https://api.flickr.com/services/
rest/?api_key=${apiKey}&method=flickr.photos.
search&format=json&nojsoncallback=1&&per_page=50
&page=1&text=${searchKeyword}`;
fetch(url)
.then(response => response.json())
.then(data => data.photos.photo.map((x) => {
this.setState({
farm: x.farm,
id: x.id,
secret: x.secret,
server: x.server})
// console.log(this.state)
}))
}
render() {
return (
<div className="App">
<Header />
<Main img={this.state.photos} />
<Navigation />
</div>
);
}
}
export default class Main extends Component {
render() {
return(
<main className="main">
{console.log(this.props.photos)}
</main>
)
}
}
Edit:
Why is this.props.img undefined first?
Screen shot from console.log(this.props.img)
fetch(url)
.then(response => response.json())
.then(data => data.photos.photo.map((x) => {
this.setState({
farm: x.farm,
id: x.id,
secret: x.secret,
server: x.server})
}))
What is happening is that your map function in your promise is resetting the component's state for every photo that is returned. So your state will always be the last object in your list of returned photos.
Here is a more simplified example of what I am referring to
const testArray = [1,2,3,4];
let currentState;
testArray.map((value) => currentState = value)
console.log(currentState);
What you want to do is this
const testArray = [1,2,3,4];
let currentState;
//Notice we are using the return value of the map function itself.
currentState = testArray.map((value) => value)
console.log(currentState);
For what you are trying to accomplish, you want your state to be the result of the map function (since that returns an array of your results from the map). Something like this:
fetch(url)
.then(response => response.json())
.then(data =>
this.setState({
photos:
data.photos.photo.map((x) => ({
farm: x.farm,
id: x.id,
secret: x.secret,
server: x.server
}))
})
)
This error might also happen if you try to provide something else other than the array that .map() is expecting, even if you declare the variable type properly. A hook-based example:
const [myTwinkies, setMyTwinkies] = useState<Twinkies[]>([]);
useEffect(() => {
// add a twinky if none are left in 7eleven
// setMyTwinkies(twinkiesAt711 ?? {}); // ---> CAUSES ".map is not a function"
setMyTwinkies(twinkiesAt711 ?? [{}]);
}, [twinkiesAt711, setMyTwinkies]);
return (<ul>
{myTwinkies.map((twinky, i)=> (
<li key={i}>Twinky {i}: {twinky?.expiryDate}</li>
))}
</ul>)
Just check the length of the array before going for the map. If the len is more than 0 then go for it, otherwise, ignore it.
data.photos.photo.map.length>0 && data.photos.photo.map(........)