How to manage depending functions in nodejs - express

Question

I am trying to teach myself nodejs and expressjs, however coming from java and c++ this is proving difficult to get used to.
I made a simple and messy module that it is supposed to return a weather forecast for a given zip code.
The way this happens is by taking the user zip code and using a google api to generate the geo coordinates for that zip code. I get the coordinates from the JASON file and then provide them to the next api call, this call is done to the forecast.io api and this time the weather data for the location is also taken from a JASON file.
Coming from java and with a not so solid background on JavaScript I am having a hard time making these two functions wait for one another, in this case I need the google api call to finish first because the coordinates it will provide are needed for the second api call. Can someone take a look at this code and tell me if the strategy I used is correct/ provide a suggestion so that I can know what is done in javascript in situations like this.
here is the code:
// The required modules.
var http = require("http");
var https = require("https");
//result object
var resultSet = {
latitude :"",
longitude:"",
localInfo:"",
weather:"",
humidity:"",
pressure:"",
time:""
};
//print out error messages
function printError(error){
console.error(error.message);
}
//Forecast API required information:
//key for the forecast IO app
var forecast_IO_Key = "this is my key, not publishing for security reasons";
var forecast_IO_Web_Adress = "https://api.forecast.io/forecast/";
//Create Forecast request string function
function createForecastRequest(latitude, longitude){
var request = forecast_IO_Web_Adress + forecast_IO_Key + "/"
+ latitude +"," + longitude;
return request;
}
//Google GEO API required information:
//Create Google Geo Request
var google_GEO_Web_Adress = "https://maps.googleapis.com/maps/api/geocode/json?address=";
function createGoogleGeoMapRequest(zipCode){
var request = google_GEO_Web_Adress+zipCode + "&sensor=false";
return request;
}
function get(zipCode){
// 1- Need to request google for geo locations using a given zip
var googleRequest = https.get(createGoogleGeoMapRequest(zipCode), function(response){
//console.log(createGoogleGeoMapRequest(zipCode));
var body = "";
var status = response.statusCode;
//a- Read the data.
response.on("data", function(chunk){
body+=chunk;
});
//b- Parse the data.
response.on("end", function(){
if(status === 200){
try{
var coordinates = JSON.parse(body);
resultSet.latitude = coordinates.results[0].geometry.location.lat;
resultSet.longitude = coordinates.results[0].geometry.location.lng;
resultSet.localInfo = coordinates.results[0].address_components[0].long_name + ", " +
coordinates.results[0].address_components[1].long_name + ", " +
coordinates.results[0].address_components[2].long_name + ", " +
coordinates.results[0].address_components[3].long_name + ". ";
}catch(error){
printError(error.message);
}finally{
connectToForecastIO(resultSet.latitude,resultSet.longitude);
}
}else{
printError({message: "Error with GEO API"+http.STATUS_CODES[response.statusCode]})
}
});
});
function connectToForecastIO(latitude,longitude){
var forecastRequest = https.get(createForecastRequest(latitude,longitude),function(response){
// console.log(createForecastRequest(latitude,longitude));
var body = "";
var status = response.statusCode;
//read the data
response.on("data", function(chunk){
body+=chunk;
});
//parse the data
response.on("end", function(){
try{
var weatherReport = JSON.parse(body);
resultSet.weather = weatherReport.currently.summary;
resultSet.humidity = weatherReport.currently.humidity;
resultSet.temperature = weatherReport.currently.temperature;
resultSet.pressure = weatherReport.currently.pressure;
resultSet.time = weatherReport.currently.time;
}catch(error){
printError(error.message);
}finally{
return resultSet;
}
});
});
}
}
//define the name of the outer module.
module.exports.get = get;
is the return statement properly placed? Is my use of finally proper in here? Please notice that I come from a java background and in java is perfectly fine to use the try{} catch(){} and finally{} blocks to execute closure code, it was the only way i managed this module to work. But now that i have incorporated some Express and I try to execute this module's method from another module, all I am getting is an undefined return.

Answer 1

You could use the Promise API, kind of like Futures in Java, so basically what you could do is wrap both functions in promises and the you could wait for resolve to execute the next function
var googleRequest = function(zipcode) {
return new Promise(function(resolve, reject) {
var request = https.get(createGoogleGeoMapRequest(zipCode), function(response) {
if (response.statusCode !== 200) {
reject(new Error('Failed to get request status:' + response.statusCode));
}
var body = "";
//a- Read the data.
response.on("data", function(chunk) {
body+=chunk;
});
//b- Parse the data.
response.on("end", function(body) {
var coordinates = JSON.parse(body);
resultSet.latitude = coordinates.results[0].geometry.location.lat;
resultSet.longitude = coordinates.results[0].geometry.location.lng;
resultSet.localInfo = coordinates.results[0].address_components[0].long_name + ", " +
coordinates.results[0].address_components[1].long_name + ", " +
coordinates.results[0].address_components[2].long_name + ", " +
coordinates.results[0].address_components[3].long_name + ". ";
resolve(resultSet);
})
});
request.on('error', function(err) {
reject(err);
});
});
}
After that you could just do
googleRequest(90210).then(function(result) {
connectToForecastIO(result.latitude, result.longitude);
}
You can find out more about Promise's usage in the Promise API docs
You should also note that there are several libraries available that allow for promise based http requests such as fetch