How to refactor this code more optimistically using Promise.all?

Question

How do we implement the below code using Promise.all() ? I have tried using promise,async/await way. But, this problem requires something to be done using Promise.all()

class Provider{
  /*
  Gets the weather for a given city
  */
  static getWeather(city){
    return Promise.resolve(`The weather of ${city} is cloudy`)
  };
  /*
  Gets the weather for a given city
  */
  static getLocalCurrency(city){
    return Promise.resolve(`The local currency of ${city} is GBP`)
  };
  /*
  Gets the Longitude and Latitude, this function returns a city
  */
  static findCity(long,lat){
    return Promise.resolve(`London`)
  };
  
};

//my implamentation;

let fnCall = async () => {
  let city = await Provider.findCity(0.1278,51.5074);
  let cityWeather = await Provider.getWeather(city);
  let cityCurrency = await Provider.getLocalCurrency(city);
  
  console.log(city);
  console.log(cityWeather);
  console.log(cityCurrency);
} 

fnCall();

Not possible, because each subsequent call depends on the previous — CertainPerformance, Jul 26 '22 at 06:40
@CertainPerformance - Not necessarily - see this [answer](https://stackoverflow.com/a/38188638/2570277) — Nick, Jul 26 '22 at 06:58

score 2 · Answer 1 · answered Jul 27 '22 at 17:27

The idea is to serially chain the dependant API calls , (output of one is input to next) and streamline/pipe the independent calls parallelly.

Rest if you're interested to stick to async await sugar-coated syntax , see below snippet example.

class Provider{
  /*
  Gets the weather for a given city
  */
  static getWeather(city){
return Promise.resolve(`The weather of ${city} is cloudy`)
  };
  /*
  Gets the weather for a given city
  */
  static getLocalCurrency(city){
return Promise.resolve(`The local currency of ${city} is GBP`)
  };
  /*
  Gets the Longitude and Latitude, this function returns a city
  */
  static findCity(long,lat){
return Promise.resolve(`London`)
  };
  
};

let fnCall = async () => {
let city = await Provider.findCity(0.1278,51.5074);
let [cityWeather, cityCurrency] = await Promise.all([Provider.getWeather(city),Provider.getLocalCurrency(city)]);
  
console.log(city);
console.log(cityWeather);
console.log(cityCurrency);
} 

fnCall();

score 1 · Answer 2 · answered Jul 26 '22 at 06:59

1

You can't do Promise.all from the outset because the 2nd and 3rd are dependent on the first. But you can still chain them, using Promise.all on the inner, and passing the city result to the end of the chain.

let fnCall = async () => {
  return await Provider
    .findCity(0.1278,51.5074)
    .then(city => {
      return Promise.all([
        city,
        Provider.getWeather(city),
        Provider.getLocalCurrency(city)
      ])
    .then(([city, weather, currency]) => {
      console.log(city);
      console.log(weather);
      console.log(currency);
    })
} 

fnCall();

answered Jul 26 '22 at 06:59

Dave Meehan

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Okay Dave, Thank you very much for your approach and suggestion. – user9151444 Jul 26 '22 at 07:20
Please don't mix `async`/`await` with `.then()` calls like this – Bergi Jul 27 '22 at 17:48
Care to explain why not? – Dave Meehan Jul 27 '22 at 21:01

How to refactor this code more optimistically using Promise.all?

2 Answers2