making multiple api calls based on the size of the array

Question

I am trying to make multiple API calls based on the information in an array. For example, I have an array of ['London', 'New York', 'Mexico', 'China', 'Tokyo']

I want to get all the weathers using open weather api. I am trying to use promise.all. I need all the data back before rendering to the front, but my code isn't working.

let cities = ['London', 'New York', 'Mexico', 'China', 'Tokyo'] 
let promisesArray = []
return new Promise(function(resolve, reject) {
    for(let i = 0; i < cities.length; i++) {

        let cities = ['London', 'New York', 'Mexico', 'China', 'Tokyo'] 
        let url = 'api.openweathermap.org/data/2.5/weather?q=' + cities[i]
        request(url, function(error, response, body){

            if (err) {
                reject(error);
            }

            var data = JSON.parse(body)
            var results = data.Search;
            promisesArray.push(resolve(results));
        });

    }
})

    Promise.all(promisesArray)
        .then(function(results) {

        })
        .catch(function(error) {

        })

Why you use return ? If inside of function, Promise.all in your code won't run. — hong4rc
– hong4rc, Commented Jul 10, 2018 at 1:44

Mark · Accepted Answer · 2018-07-10 02:27:22Z

You have a couple things mixed up but it's the right idea. Your promiseArray needs to contain promises, not the data.

So you should go through your cities, create a promise for each, inside the promise call request and when the request returns call resolve. This is a little cleaner with array.map than a for loop.

Here's an example with a mocked request function:

// fakes request
function request(url, cb) {
  setTimeout(() => cb(null, 200, `{"Search": "success for ${url}" }`), 200)
}


let cities = ['London', 'New York', 'Mexico', 'China', 'Tokyo']

// promisesArray will hold all the promises created in map()
let promisesArray = cities.map(city => {
  // make a new promise for each element of cities
  return new Promise((resolve, reject) => {
    let url = 'http://api.openweathermap.org/data/2.5/weather?q=' + city
    request(url, function(error, response, body) {
      if (error) {
        reject(error);
      }
      var data = JSON.parse(body)
      var results = data.Search;
      // resolve once we have some data
      resolve(results);
    });
  })
})

Promise.all(promisesArray)
  .then(function(results) {
    console.log(results)
  })
  .catch(function(error) {
    console.log(error)
  })

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