I am pretty much familiar with the async await but with back end nodejs. But there is a scenario came across to me where I have to use it on front end.
I am getting array of objects and in that objects I am getting lat lng of the places. Now using react-geocode I can get the place name for a single lat lng but I want to use that inside the map function to get the places names. SO as we know it async call I have to use async await over there.
Here is the code
import Geocode from "react-geocode";
render = async() => {
const {
phase,
getCompanyUserRidesData
} = this.props
return (
<div>
<tbody>
await Promise.all(_.get(this.props, 'getCompanyUserRidesData', []).map(async(userRides,index) => {
const address = await Geocode.fromLatLng(22.685131,75.873468)
console.log(address.results[0].formatted_address)
return (
<tr key={index}>
<td>
{address.results[0].formatted_address}
</td>
<td>Goa</td>
<td>asdsad</td>
<td>{_.get(userRides,'driverId.email', '')}</td>
<td>{_.get(userRides,'driverId.mobile', '')}</td>
</tr>
)
}))
</tbody>
</div>
)
}
But when I use async with the map function here it doesn't return anything. Can anyone please help me where I going wrong?
You should always separate concerns like fetching data from concerns like displaying it. Here there's a parent component that fetches the data via AJAX and then conditionally renders a pure functional child component when the data comes in.
class ParentThatFetches extends React.Component {
constructor () {
this.state = {};
}
componentDidMount () {
fetch('/some/async/data')
.then(resp => resp.json())
.then(data => this.setState({data}));
}
render () {
{this.state.data && (
<Child data={this.state.data} />
)}
}
}
const Child = ({data}) => (
<tr>
{data.map((x, i) => (<td key={i}>{x}</td>))}
</tr>
);
I didn't actually run it so their may be some minor errors, and if your data records have unique ids you should use those for the key attribute instead of the array index, but you get the jist.
UPDATE
Same thing but simpler and shorter using hooks:
const ParentThatFetches = () => {
const [data, updateData] = useState();
useEffect(() => {
const getData = async () => {
const resp = await fetch('some/url');
const json = await resp.json()
updateData(json);
}
getData();
}, []);
return data && <Child data={data} />
}
With the wrapper function below, delayed_render(), you can write asynchronous code inside a React component function:
function delayed_render(async_fun, deps=[]) {
const [output, setOutput] = useState()
useEffect(async () => setOutput(await async_fun()), deps)
return (output === undefined) ? null : output
}
This wrapper performs delayed rendering: it returns null on initial rendering attempt (to skip rendering of this particular component), then asynchronously calculates (useEffect()) the proper rendering output through a given async_fun() and invokes re-rendering to inject the final result to the DOM. The use of this wrapper is as simple as:
function Component(props) {
return delayed_render(async () => { /* any rendering code with awaits... */ })
}
For example:
function Component(props) {
return delayed_render(async () => {
const resp = await fetch(props.targetURL) // await here is OK!
const json = await resp.json()
return <Child data={json} />
})
}
UPDATE: added the deps argument. If your async_fun depends on props or state variables, all of them must be listed in deps to allow re-rendering. Note that passing deps=null (always re-render) is not an option here, because the output is a state variable, too, and would be implicitly included in dependencies, which would cause infinite re-rendering after the async_fun call completes.
This solution was inspired by, and is a generalization of, the Jared Smith's one.
Related
I'm using the YTS API and I need to change the link for the call, I have to use
?query_term= and add the text that the user is typing, for autocomplete. I'm using mantine components for the autocomplete. I tried putting the call inside the handlechange function, but this is not possible.
const [movieNames, setMovieNames] = useState([])
const onChangeHandler = (text) => {
useEffect(() => {
const loadMovieNames = async () => {
const response = await axios.get('https://yts.mx/api/v2/list_movies.json?query_term='+text);
let arrayOfMoviesNames = [];
response.data.data.movies.forEach(i => {
arrayOfMoviesNames.push(i.title)
});
setMovieNames(arrayOfMoviesNames)
}
loadMovieNames()
}, [])
}
.
<Autocomplete
placeholder="Search Movie"
limit={8}
data={movieNames}
onChange={e => onChangeHandler(e.target.value)}
/>
You MUST use hooks in the execution context of Function Component, you used the useEffect inside a function not in the execution context of Function Component.
const YourComponent = () => {
const [movieNames, setMovieNames] = useState([]);
const loadMovieNames = async (text) => {
const response = await axios.get(
'https://yts.mx/api/v2/list_movies.json?query_term=' + text
);
let arrayOfMoviesNames = [];
response.data.data.movies.forEach((i) => {
arrayOfMoviesNames.push(i.title);
});
setMovieNames(arrayOfMoviesNames);
};
return (
<Autocomplete
placeholder="Search Movie"
limit={8}
data={movieNames}
onChange={(value) => loadMovieNames(value)}
/>
);
};
It is also possible without useEffect, so without making it so complicated by using useEffect and onChangeHandler both, only use onChangeHandler function to update the movieNames and it will automatically update the DOM texts (I mean where ever you use)...
import React, { useState } from "react";
function MoviesPage(props) {
const [ movieNames, setMovieNames ] = useState([]);
const [ searchValue, setSearchValue ] = useState("");
const onChangeHandler = async (text) => {
const response = await axios.get(
'https://yts.mx/api/v2/list_movies.json?query_term=' + text
);
let arrayOfMoviesNames = [];
response.data.data.movies.forEach(i => {
arrayOfMoviesNames.push(i.title)
});
setMovieNames(arrayOfMoviesNames);
}
return (
<div>
<Autocomplete
placeholder="Search Movie"
limit={8}
data={movieNames}
onChange={(e) => onChangeHandler(e.target.value)}
/>
</div>
);
}
export default MoviesPage;
...and just to clarify, you can use useEffect in case of API if you want to initialize the page with the API data. You can use this hook if you don't have any onChange handlers. Another way you can approach is you can update a state hook (like searchData) on the change of the Search Bar, and lastly add the the searchData variable to the useEffect dependency array:
useEffect(() => {
// use the searchData variable to populate or update the page
// ...
},
[
searchData, // <-- talking about this line
]);
So, this was my solution. Hope this helps you mate!
useEffect is a hook, which executes on state change, So keep the useEffect funtion outside the onChangeHandler and add a new state for 'query param' and setQueryState(text) inside the onChangeHandler, and put the state param as dependency in useEffect, So whenever this state gets changed this will call the use effect function automatically.
I am trying to render a component within a component file that relies on data from an outside API. Basically, my return in my component uses a component that is awaiting data, but I get an error of dataRecords is undefined and thus cannot be mapped over.
Hopefully my code will explain this better:
// Component.js
export const History = () => {
const [dateRecords, setDateRecords] = useState(0)
const { data, loading } = useGetRecords() // A custom hook to get the data
useEffect(() => {
fetchData()
}, [loading, data])
const fetchData = async () => {
try {
let records = await data
setDateRecords(records)
} catch (err) {
console.error(err)
}
}
// Below: Render component to be used in the component return
const GameItem = ({ game }) => {
return <div>{game.name}</div>
}
// When I map over dateRecords, I get an error that it is undefined
const renderRecords = async (GameItem) => {
return await dateRecords.map((game, index) => (
<GameItem key={index} game={game} />
))
}
const GameTable = () => {
return <div>{renderRecords(<GameItem />)}</div>
}
return(
// Don't display anything until dateRecords is loaded
{dateRecords? (
// Only display <GameTable/> if the dateRecords is not empty
{dateRecords.length > 0 && <GameTable/>
)
)
}
If dateRecords is meant to be an array, initialize it to an array instead of a number:
const [dateRecords, setDateRecords] = useState([]);
In this case when the API operation is being performed, anything trying to iterate over dateRecords will simply iterate over an empty array, displaying nothing.
You've set the initial state of dateRecords to 0 which is a number and is not iterable. You should set the initial state to an empty array:
const [dateRecords, setDateRecords] = useState([]);
I am using React context to pass down data, following the docs, however I am stuck with the initial value and am not sure what I did wrong.
This is what my context file looks like:
export const ItemsContext = createContext([]);
ItemsContext.displayName = 'Items';
export const ItemsProvider = ({ children }) => {
const [items, setItems] = useState([]);
const [loading, setLoading] = useState(false);
const setData = async () => {
setLoading(true);
setItems(await getItemsApiCall());
setLoading(false);
};
useEffect(() => {
setData();
}, []);
console.warn('Items:', items); // This shows the expected values when using the provider
return (
<ItemsContext.Provider value={{ items, loading }}>
{children}
</ItemsContext.Provider>
);
};
Now, I want to feed in those items into my app in the relevant components. I am doing the following:
const App = () => {
return (
<ItemsContext.Consumer>
{(items) => {
console.warn('items?', items); // Is always the initial value of "[]"
return (<div>Test</div>);
}}
</ItemsContext.Consumer>
);
}
However, as my comment states, items will always be empty. On the other hands, if I do just use the ItemsProvider, I do get the proper value, but at this point need to access it directly on the app, so the ItemsContext.Consumer seems to make more sense.
Am I doing something wrong here?
Edit: A way around it seems to be to wrap the Consumer with the Provider, but that feels wrong and didn't see that at the docs. Is that perhaps the case?
So essentially, something like this:
const App = () => {
return (
<ItemsProvider>
<ItemsContext.Consumer>
{(items) => {
console.warn('items?', items); // Is always the initial value of "[]"
return (<div>Test</div>);
}}
</ItemsContext.Consumer>
</ItemsProvider>
);
}
You have to provide a ItemsContext provider above the App component hierarchy,otherwise the default value of the context will be used.
something in this form:
<ItemsContext.Provider value={...}>
<App/>
</ItemsContext.Provider>
I have a react component using Hooks where I click a button to make API calls to the Hacker News API and push the results into an array. Then I set the state of "stories" to be that array full of stories.
I have a second function fired off by a button which console logs the state of "stories" and console.log's a .map returning each stories title. All of this works just fine.
If I attempt to use a .map in the return of the component it does not work. If I initalize the state of "stories" to be ["test", "test1", "test2"] the .map works but as soon as I hit my button to set the state to be the array of stories the .map stops working. No error messages just the content goes away.
Here is where I import React and set the initial state, I've used Axios, Fetch and Wretch to make the API calls, all with the same results:
import React, { useState, useEffect } from 'react';
const axios = require('axios');
import wretch from "wretch"
function App () {
const [stories, setStories] = useState(["test", "test2", "test3"]);
Here is the function that I fire off to hit the API andf set the state:
function call () {
let storiesArr = [];
fetch('http://hacker-news.firebaseio.com/v0/topstories.json')
.then ((res) => res.json())
.then ((data) => {
for (let i = 0; i < 20; i++) {
fetch(`http://hacker-news.firebaseio.com/v0/item/${data[i]}.json`)
.then((res) => res.json())
.then((eachStory) => {
storiesArr.push(eachStory);
})
}
})
Here is a second function that I'm using to check that state was set with what I think it was and to make sure that a .map works on the state of "stories". This does work for me:
function test () {
console.log(stories);
stories.map((each) => {
return <p>{each.title}</p>
})
}
This is my return, the .map here does work with the initial state but does not once I set state to be the new array:
return (
<>
<h1 onClick={ () => call() } className="click">Fire off API calls</h1>
<h1 onClick={ () => test() } className="click">Test state of stories/<br/>.map each title</h1>
<table className="table">
<thead>
<tr>
<td>Table</td>
</tr>
</thead>
<tbody>
{
stories.map((each, i) => {
return <tr key={i}>
<td>{each.title ? each.title : each}</td>
</tr>
})
}
</tbody>
</table>
</>
);
I am unable to figure out why the .map works at first, no longer works in the return, but does work in a function....
I would greatly appreciate any help any one can be.
Your data fetching look a little messy, you know you can use Promise.all instead of pushing to an array and looping.
I have added a check to see if the component is still mounted before setting state.
const isMounted = useIsMounted();
//other code, I imagine useEfffect
function call() {
fetch(
'http://hacker-news.firebaseio.com/v0/topstories.json'
)
.then(res => res.json())
.then(data =>
Promise.all(
data.map(item =>
fetch(
`http://hacker-news.firebaseio.com/v0/item/${item}.json`
).then(res => res.json())
)
)
)
.then(
result => isMounted.current && setStories(result)
);
}
Also: http://hacker-news.firebaseio.com/v0/topstories.json returns over 400 items, that will cause you to make over 400 requests for each item, I don't think hacker-news will appreciate that so maybe slice the result and or page it.
I think this is more of an async processing issue than a setState one. Here is a handy all in one (simplified) example
import React, { useState } from "react";
import ReactDOM from "react-dom";
// gets list of article ids
const getStoryList = async () => {
const res = await fetch(
"https://hacker-news.firebaseio.com/v0/topstories.json"
);
return await res.json();
};
// iterates over article list and returns a promise.all
const getStories = (articles, quantity) => {
return Promise.all(
articles.slice(0, quantity).map(async article => {
const storyRes = await fetch(
`https://hacker-news.firebaseio.com/v0/item/${article}.json`
);
return await storyRes.json();
})
);
};
// maps your response data
const formatStories = stories =>
stories.map(({ by, id, url, title = "No Title" }) => ({
id,
title,
url,
by
}));
function App() {
const [stories, setStories] = useState([]);
const call = async () => {
// first get list of stories
const res = await getStoryList();
// then async request all of the individual articles
// and push them into a group of promises
const storiesArr = await getStories(res, 20);
// then set your state.
setStories(formatStories(storiesArr));
};
return (
<div className="App">
<button onClick={call} className="click">
Fire off API calls
</button>
<table className="table">
<thead>
<tr>
<td>Table</td>
</tr>
</thead>
<tbody>
{stories.map(story => {
return (
<tr key={story.id}>
<td>
<a href={story.url}>{story.title}</a> by {story.by}
</td>
</tr>
);
})}
</tbody>
</table>
</div>
);
}
const rootElement = document.getElementById("root");
ReactDOM.render(<App />, rootElement);
Summary
I have the following function inside of a functional component which keeps coming back undefined. All of the data inside the function, tableData and subtractedStats are defined and accurate.
This is probably just a small JavaScript I'm making so your help would be greatly appreciated!
Code
This is a functional component below:
const TableComponent = ({ tableData }) => {
formatTableData = () => {
console.log("inside sumDataFormat", tableData);
return tableData.forEach(competitor => {
let subtractedStats = [];
console.log("competitor in", competitor);
for (const i in competitor.startingLifeTimeStats) {
if (competitor.startingLifeTimeStats[i]) {
competitor.stats
? (subtractedStats[i] =
competitor.stats[i] - competitor.startingLifeTimeStats[i])
: (subtractedStats[i] = 0);
}
}
console.log("subtractedStats", subtractedStats);
return subtractedStats;
});
};
useEffect(() => {
console.log("formatTableData", formatTableData());
});
}
Edit:
Can someone help me to what's wrong in this code (how to solve this?) and could briefly explain a functional component
The forEach function doesn't not return anything, it simply iterates over your array, giving you an undefined, the map function could be what you were looking for :
formatTableData = () => {
console.log("inside sumDataFormat", tableData);
return tableData.map(competitor => { // This returns another array where every element is converted by what's returned in the predicate
Functional Component are the most basic kind of React component, defined by the component's (unchanging) props.
Functional Component needs return some JSX code (UI) (can be null too).
Here's an example of most basic Functional Component
const App = () => {
const greeting = 'Hello Function Component!';
return <Headline value={greeting} />;
};
const Headline = ({ value }) => {
return <h1>{value}</h1>;
};
export default App;
Solution Code
Here's the solution of the above example as a Functional Component
This is solution below uses hooks to save data to component's state and also uses lifecycle methods to parse that data on componentDidMount:
const TableComponent = (props: ) => {
const [state, setState] = useState(initialState)
// componentDidUpdate
useEffect(() => {
setState(getData(props.data));
}, []);
// getData() - Parser for data coming inside the functional Component
const getData = (tableData) => {
return tableData.map(competitor => {
return competitor.startingLifeTimeStats.map((item, index) => {
return item && competitor.stats ? competitor.stats[index]-item : 0;
})
})
};
// UI (JSX)
return (
<Text>{JSON.stringify(state)}</Text>
);
}
export default TableComponent;
Try with map sample code as below.
render() {
return (<div>
{this.state.people.map((person, index) => (
<p>Hello, {person.name} from {person.country}!</p>
))}
</div>);
}