I have created a Home.js and included inside App.js of my react app.I want to fetch json data but I am getting the following error-
My Code- https://stackblitz.com/edit/react-kwaooy?file=src/App.js
For initial load your this.state.lists.regionData will be undefined and you are accessing the undefined value that might be the issue for crashing the application.
Change your state value like below,
this.state = {
lists: {
regionData: [],
activeCases: '',
activeCasesNew: '',
deaths: ''
}
};
You need to check what you are actually storing in the list state from the response. What I see is that you are storing response.data but you might actually want to store regionData from the response. This will allow map to iterate over the regionData values and not show this error.
Related
I am receiving the following error when I call inside getStaticProps and I cannot figure out why:
Error: Error serializing `.lingo` returned from `getStaticProps` in "/".
Reason: `undefined` cannot be serialized as JSON.
I've placed the full app code on CodeSandbox. It won't be able to access the API but it does show where things are defined.
When I run the following query on GraphQL playground I get the expected response:
query {
allTerms {
id
term
slug
lead
}
}
You can see that this query is contained in lingo.service.js in the modules/lingo/services directory on the sandbox but the homepage has the Error serializing error. Is my function export async function getAll() not correct or am I calling it wrong in getStaticProps?
await getAll() is most likely returning undefined which is not serializable JSON. Defaulting to null would be one way to solve the issue.
export async function getStaticProps(context) {
return {
props: { lingo: (await getAll()) ?? null },
};
}
Right, this is supposed to be more of a comment but apparently I don't have enough reputation points to comment. So, I'll answer it like this.
Just check if your props (under getStaticProps()) are named correctly i.e. how they're named in the .json file you're trying to read. I ran into this issue because of a typo I had and just fixed it.
I was using OMDBapi to get the details of different movies. I successfully fetched the result and it returns a json object like this;
{"Title":"WWA: The Inception","Year":"2001","Rated":"N/A","Released":"26 Oct 2001","Runtime":"N/A","Genre":"Action, Sport","Director":"N/A","Writer":"Jeremy Borash","Actors":"Bret Hart, Jeff Jarrett, Brian James, David Heath","Plot":"N/A","Language":"English","Country":"Australia","Awards":"N/A","Poster":"https://m.media-amazon.com/images/M/MV5BNTEyNGJjMTMtZjZhZC00ODFkLWIyYzktN2JjMTcwMmY5MDJlXkEyXkFqcGdeQXVyNDkwMzY5NjQ#._V1_SX300.jpg","Ratings":[{"Source":"Internet Movie Database","Value":"6.0/10"}],"Metascore":"N/A","imdbRating":"6.0","imdbVotes":"22","imdbID":"tt0311992","Type":"movie","DVD":"N/A","BoxOffice":"N/A","Production":"N/A","Website":"N/A","Response":"True"}
Note that we get this type of object from the api if we want to get a particular movie details and that is what i was doing. Now to show the different details to a user, i started parsing this JSON object which works fine but when i try to get the value of the Value key present inside the Ratings key, it returns undefined.
I am working with react-native. After getting the data, i stored it inside the state, named it as details. Then to get it;
this.state.details.Title //if i wanted to get the Title and it works fine.
Then for Value inside Ratings;
this.state.details.Ratings[0].Value
But it returns undefined.
Also note that this works fine in pure Javascript as i parsed the dict in the browser console in the same way and it returned the correct value.
Here is more code;
componentDidMount() {
this.fetchData();
}
fetchData = async () => {
const response = await fetch(`http://www.omdbapi.com/?i=${this.props.navigation.getParam('i')}&apikey=******`) // where this.props.navigation.getParam('i') is the omdbid of the movie
const result = await response.json()
this.setState({details: result})
}
Here is error log;
undefined is not an object (evaluating 'this.state.details.Ratings[0]')
You're most likely trying to access state object before fetch has done it's job .... it's an async op ... so you should make sure your data is ready before rendering...
if (this.state.details) {
// start rendering...
}
More Explanation
your setState function should be executed right after fetch has finished its job, and since it's an async operation, it's going to take some time ...During that time, render function is executed with no state.details --> causing your issue ...
That's why you should check for state before rendering ... besides, the optional chaining trick Silversky Technology mentioned in his answer
If the value property you are accessing from the object might be not available for all the movies in the data you are getting from API response so it might cause you to error when accessing key from undefined objects.
To overcome the issue there is a way, you can try a fix as below:
this.state.details.Ratings[0]?.Value
The ? symbol lets the javascript not give an error when the value key not available in the object. it will make the accessing of property optional.
When storing objects in states it often causes problems as you are doing in line
this.setState({details: result})
Save result after strigifying it like
JSON.stringify(result)
this.setState({details: result})
Then when fetching form state, parse it back to object by
var result = JSON.parse(this.state.details)
Then you should be able to access it
You can access Ratings[0].Value by
this.state.details.Ratings && this.state.details.Ratings[0].Value
like,
<Text> {this.state.details.Ratings && this.state.details.Ratings[0].Value} </Text>
There are similar questions out there on StackOverflow but not exactly like mine.
When I check the Network tab in Inspector the data is being pulled from the api service. However, when I try to call it to the page I get [object][object].
Here's the structure of the data:
Object.widget.Value ... I would like to display the Value.
Here's how I am currently trying to call it:
{{i.widget}}
I've also tried json stringify and "| json" and those get me "undefined".
All other data that exists on the same level as widget is displaying fine and formatted the same. For some reason I can't pull widget's value.
Thanks for the help!
if this's what API return to us:
{name: "fox"}
in our component we can get it as:
data: any;
this.service.getData().subscribe((response) => {
this.data = response.body;
});
in our view if we put {{data}} it will return [object][object], you should set an property too in this case we have name which equal to fox, for example: {{data.name}};
I ran a api and get the json object of object. Below is the screenshot of that object. In react native, I am getting this data in component from redux with the key "data".
When I try to fetch city name in mapStateToProps component, I am getting this error
TypeError: Cannot read property 'name' of undefined
Blockquote
my mapStateToProps is below.
const mapStateToProp = ({data}) => {
//console.log(data);
return {
city: data.data.city.name
}
}
I am getting complete data to city but unable to access its name property Why?
Since you're getting the data from a fetch request the city property probably doesn't exist before the request. Try preventing the error by checking if the city exists when you set the value in mapStateToProps
const mapStateToProp = ({data}) => {
//console.log(data);
return {
city: data.data.city ? data.data.city.name : null
}
}
Keep in mind that it is also a good practice to not have deeply nested data in your store.
This is a slightly messy questions. Although it appears I'm asking question about amCharts, I really just trying to figure how to extract an array from HTTP request and then turn it into a variable and place it in to 3-party javacript.
It all starts here, with this question, which was kindly answered by AmCharts support.
As one can see from the plnker. The chart is working. Data for the chart is hard coded:
`var chartData = [{date: new Date(2015,2,31,0,0,0, 0),value:372.10,volume:2506100},{date: new Date(2015,3,1,0, 0, 0, 0),value:370.26,volume:2458100},{date: new Date(2015,3,2,0, 0, 0, 0),value:372.25,volume:1875300},{date: new Date(2015,3,6,0, 0, 0, 0),value:377.04,volume:3050700}];`
So we know the amCharts part works. Know where the problem is changing hard coded data to a json request so it can be dynamic. I don't think this should be tremendously difficult, but for the life of me I can't seem figure it out.
The first issue is I can't find any documentation on .map, .subscribe, or .observable.
So here is a plunker that looks very similar to the first one, however it has an http providers and injectable. It's broken, because I can't figure out how to pull the data from the service an place it into the AmCharts function. I know how pull data from a http provider and display it in template using NgFor, but I don't need it in the template (view). As you can see, I'm successful in transferring the data from the service, with the getTitle() function.
this.chart_data =_dataService.getEntries();
console.log('Does this work? '+this.chart_data);
this.title = _dataService.getTitle();
console.log('This works '+this.title);
// Transfer the http request to chartData to it can go into Amcharts
// I think this should be string?
var chartData = this.chart_data;
So the ultimate question is why can't I use a service to get data, turn that data into a variable and place it into a chart. I suspect a few clues might be in options.json as the json might not be formatted correctly? Am I declaring the correct variables? Finally, it might have something to do with observable / map?
You have a few things here. First this is a class, keep it that way. By that I mean to move the functions you have inside your constructor out of it and make them methods of your class.
Second, you have this piece of code
this.chart_data =_dataService.getEntries().subscribe((data) => {
this.chart_data = data;
});
What happens inside subscribe runs asynchronously therefore this.chart_data won't exist out of it. What you're doing here is assigning the object itself, in this case what subscribe returns, not the http response. So you can simply put your library initialization inside of the subscribe and that'll work.
_dataService.getEntries().subscribe((data) => {
if (AmCharts.isReady) {
this.createStockChart(data);
} else {
AmCharts.ready(() => this.createStockChart(data));
}
});
Now, finally you have an interesting thing. In your JSON you have your date properties contain a string with new Date inside, that's nothing but a string and your library requires (for what I tested) a Date object, so you need to parse it. The problem here is that you can't parse nor stringify by default a Date object. We need to convert that string to a Date object.
Look at this snippet code, I used eval (PLEASE DON'T DO IT YOURSELF, IS JUST FOR SHOWING PURPOSES!)
let chartData = [];
for(let i = 0; i < data[0].chart_data.length; i++) {
chartData.push({
// FOR SHOWING PURPOSES ONLY, DON'T TRY IT AT HOME
// This will parse the string to an actual Date object
date : eval(data[0].chart_data[i].date);
value : data[0].chart_data[i].value;
volume : data[0].chart_data[i].volume;
});
}
Here what I'm doing is reconstructing the array so the values are as required.
For the latter case you'll have to construct your json using (new Date('YOUR DATE')).toJSON() and you can parse it to a Date object using new Date(yourJSON) (referece Date.prototype.toJSON() - MDN). This is something you should resolve in your server side. Assuming you already solved that, your code should look as follows
// The date property in your json file should be stringified using new Date(...).toJSON()
date : new Date(data[0].chart_data[i].date);
Here's a plnkr with the evil eval. Remember, you have to send the date as a JSON from the server to your client and in your client you have to parse it to a Date.
I hope this helps you a little bit.
If the getEntries method of DataService returns an observable, you need to subscribe on it to get data:
_dataService.getEntries().subscribe(
(data) => {
this.chart_data = data;
});
Don't forget that data are received asynchronously from an HTTP call. The http.get method returns an observable (something "similar" to promise) will receive the data in the future. But when the getEntries method returns the data aren't there yet...
The getTitle is a synchronous method so you can call it the way you did.