CODEWITHSUNDEEP
javascriptreactjsgoogle-mapspromisegoogle-geocoder
Basik
Basik

Reputation: 65

ReactJS -> store variable from promise

I'm trying to figure out how to store promise return stages into variables. In this use case, I'm using google maps and google's geocoder to transform a JSON file of addresses into an array of lat lng objects in order to make markers, but I'm curious regardless. It's been done through a single promise, but as I'm forced to loop through the data and execute the call, I can't call another function and leave the promise, as I have to repeat the promise eventually. This means I need to store the object in a separate variable. See the sections of code below.

address.json

{ 
  "address" : "Oosterpark 9",
  "city" : "Amsterdam",
  "name" : "Onze Lieve Vrouwe Gasthuis"
  "zipcode" : "1091 AC"
},
{
  "address" : "Jan Tooropstraat 164",
  "city" : "Amsterdam",
  "name" : "Sint Lucas Andreas Hospital"
  "zipcode" : "1061 AE"
}

Map.js

makeMarker(a){
    Geocode.setApiKey(this.apiKey);
    let arr = [];
    for(let i=0; i < a.length; i++){
        let address = b[i].address.replace(" ","+") + ',+'+b[i].zipcode.replace(" ","+")+',+'+b[i].city;

        arr[i] = Geocode.fromAddress(address).then(
            response => {
                const {lat, lng} = response.results[0].geometry.location;
                console.log(lat, lng);
                return {lat: lat, lng: lng};
            }
        );
    }
return arr;
}

In this case the above function is called on in the constructor where a variable is waiting to be defined by the outcome of the makeMarker function. In this case, it only returns [promise, promise], when it's supposed to return [{lat: __, lng: __,}, {lat: __, lng: __,}].

I hope to hear some of your ideas on how to solve this use case!

Upvotes: 3

Views: 2677

Answers (2)

Sagiv b.g
Sagiv b.g

Reputation: 31024

You can use Promise.all, create an array of promises on the instance of the class, then on componentDidMount (or other useful life cycle hook) run: 

Promise.all(promies).then(...)

So something like this: 

makeMarker(a){
    Geocode.setApiKey(this.apiKey);
    let arr = [];
    for(let i=0; i < a.length; i++){
        let address = b[i].address.replace(" ","+") + ',+'+b[i].zipcode.replace(" ","+")+',+'+b[i].city;

        arr[i] = Geocode.fromAddress(address)
    }
    this.promises = arr;
}

Then elsewhere in your code: 

Promise.all(this.promises).then(
  listOfResponses => {
     // rest of your code
  }
)

Here is a small example of such usage with Promise.all

const data = [1, 2, 3, 4, 5, 6];

class App extends React.Component {
  constructor(props) {
    super(props);
    this.state = {
      fetchedData: []
    }
    this.promises = data.map(d => {
      return new Promise((resolve) => {
        setTimeout(() => resolve(d),1500);
      })
    });
  }

  componentDidMount() {
    Promise.all(this.promises).then(fetchedData => this.setState({ fetchedData }));
  }
  
  render() {
    const { fetchedData } = this.state;
    return (
      <div>
        {fetchedData.length ? fetchedData.map(d => <div>{d}</div>) : "Loading..."}
      </div>
    );
  }
}

const rootElement = document.getElementById("root");
ReactDOM.render(<App />, rootElement);
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/15.1.0/react.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/15.1.0/react-dom.min.js"></script>
<div id="root"></div>

Upvotes: 2

Amaresh
Amaresh

Reputation: 81

@Sagiv b.g' s answer of using Promise.all is the best way. Here is another approach.

var arr = [];
makeMarker(a){
    Geocode.setApiKey(this.apiKey);
   
    for(let i=0; i < a.length; i++){
        let address = b[i].address.replace(" ","+") + ',+'+b[i].zipcode.replace(" ","+")+',+'+b[i].city;

        Geocode.fromAddress(address).then(
            response => {
                const {lat, lng} = response.results[0].geometry.location;
                console.log(lat, lng);
                 addToArr({lat: lat, lng: lng},b);
            }
        );
    }

}

addToArr(latLongObj,b){
  arr.push(latLongObj);
  if(arr.length >= b.length){
    //callYourfunction and do the logic
  }
}

Upvotes: 0

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