CODEWITHSUNDEEP
javascriptnode.js
Edoardo
Edoardo

Reputation: 19

Get out the information from the function

How can i get out the information from the function? Because when i start the file into the terminal, the 

console.log(latitude1 + " " + longitude1);

return me "undefined", instead when i put the

 console.log(latitude1 + " " + longitude1);

in the function, returns me the longitue and the latitude. 

var triangulate = require('wifi-triangulate')

var latitude1;
var longitude1;

triangulate(function (err, location) {
  //if (err) throw err
  var latitude = location.lat;
  var longitude = location.lng;
  latitude1 = latitude;
  longitude1 = longitude;
});
  console.log(latitude1 + " " + longitude1);

Upvotes: 0

Views: 58

Answers (2)

num8er
num8er

Reputation: 19372

You cannot just run asynchronous (non-blocking) function and after function check for result.

Because JS does not wait (does not block execution) when triangulate function will finish and go to next line.

For newbies I'll tell that it's something like ajax call in jquery.

Check this example:

var async = require('async');
var triangulate = require('wifi-triangulate');

function doSomethingWithLocation(location, cb) {
  console.log(location);
  // save to db and etc operations here
  cb();
}

async.waterfall([
  triangulate,
  doSomethingWithLocation
]);

console.log('Here goes triangulate result:'); // while `triangulate` will work, it will output message before that triangulate will pass result to `doSomethingWithLocation`



If You want to continuously get location data and operate on it, checkout this example:

1) We create component called location and put our desired functionality inside of it

components/location.js:

var triangulate = require('wifi-triangulate');

module.exports = function(callback) {
  triangulate(function(err, location) {
    if(err) {
      console.error(err);
      return callback({});
    }

    callback(location);
  });
}

2) In app file we require this component and use it and app.js:

var async = require('async');
var getLocation = require('./components/location');

var latitude, longitude;

function handleLocation(lat, lon) {
  console.log('Got location information:', lat, lon);

  // You can add here db query to update/insert info to db
}


getLocation(function(data) {
  latitude = data.lat;
  longitude = data.lng;
  handleLocation(latitude, longitude);
});

console.log('You cannot see lat, lon', latitude, longitude);
console.log('Because You\'ve to wait for execution of getLocation to complete');

Upvotes: 1

Medet Tleukabiluly
Medet Tleukabiluly

Reputation: 11930

triangulate package written in callback style, you can convert it to async, or use as it is

callback

var triangulate = require('wifi-triangulate')

function myTriangulate(callback) {
  triangulate(function (err, location) {
    if (err) throw err;
    callback(location);
  });
}

myTriangulate(function(loc) {
  console.log(loc.latitude + " " + loc.longitude); 
});

async

var triangulate = require('wifi-triangulate')
//use default node's promise lib
//or similar libs like bluebird

function myTriangulate() {
  return new Promise(function(resolve, reject) {
    triangulate(function (err, location) {
      if (err) return reject(err);
      resolve(location);
    });
  }); 
}

myTriangulate().then(function(loc) {
  console.log(loc.latitude + " " + loc.longitude); 
});

Upvotes: 1

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