Calling async functions recursively

Question

I need to have an async method eg. getWeather called forever with a small delay between the success of previous call and beginning of the next call. I have used a recursive function for the purpose. I am concerned if this can cause a performance hit. Are there any better ways to do this?

var request = require('request');
var Promise = require('bluebird');

var delayTwoSecs = function() {
    return new Promise(function(resolve, reject) {
        setTimeout(function() {
            resolve();
        }, 2000);
    });
};

var getWeather = function() {
    return new Promise(function(resolve, reject) {
        request({
            method: 'GET',
            uri: 'http://api.openweathermap.org/data/2.5/weather?lat=35&lon=139'
        }, function(error, response, body) {
            if (error) {
                reject(error);
            } else {
                resolve(body)
            }
        });
    });
};

var loopFetching = function() {
    getWeather()
        .then(function(response) {
            console.log(response);
            return delayTwoSecs();
        }).then(function(response) {
            loopFetching();
        });
};

loopFetching();

Community · Accepted Answer · 2017-05-23 12:28:24Z

3

You don't need the delayTwoSecs function, you can use the Promise.delay function.
Instead of getWeather, you can use the bluebird to Promisify all the functions and use the proper function, in this case getAsync, directly.

So, your program becomes like this

var Promise = require('bluebird');
var request = Promise.promisifyAll(require('request'));
var url = 'http://api.openweathermap.org/data/2.5/weather?lat=35&lon=139';

(function loopFetching() {
    request.getAsync(url)
         // We get the first element from the response array with `.get(0)`
        .get(0)
         // and the `body` property with `.get("body")`
        .get("body")
        .then(console.log.bind(console))
        .delay(2000)
        .then(loopFetching)
        .catch(console.err.bind(console));
})();

This is called Immediately Invoking Function Expression.

edited May 23, 2017 at 12:28

CommunityBot

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answered Mar 2, 2015 at 7:20

thefourtheye

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3 Comments

Cyril Over a year ago

This is functionally and peformance-wise same as the code in the question right?

JLRishe Over a year ago

@Cyril I don't see any reason to be concerned about performance in either approach.

Benjamin Gruenbaum Over a year ago

You can change .then(function(response){ response[0].body } with .get(0).get("body").then(function(body){ ... Also - might as well chain promises.

FactoryAidan · Accepted Answer · 2015-03-02 07:21:03Z

-1

setInterval() for recurring requests

You're over-complicating it with nested calls. Use setInterval() instead.

var request = require('request');
var Promise = require('bluebird');

var getWeather = function() {
    return new Promise(function(resolve, reject) {
        request({
            method: 'GET',
            uri: 'http://api.openweathermap.org/data/2.5/weather?lat=35&lon=139'
        }, function(error, response, body) {
            if (error) {
                reject(error);
            } else {
                resolve(body)
            }
        });
    });
};

var my_interval = setInterval("getWeather()",2000);

answered Mar 2, 2015 at 7:21

FactoryAidan

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4 Comments

Cyril Over a year ago

I needed the next call to be initiated only if the previous call was successful. And I also need to make sure the there is a constant delay in the interim. setInterval won't take care of the above two cases I guess..

JLRishe Over a year ago

Oh my. Why are you using a string in setInterval()?

FactoryAidan Over a year ago

@JSRishe have you ever tried to build a setInterval() command dynamically? That is how you do it.

Bergi Over a year ago

@FactoryAidan: No it's not. I doubt this even works, as getWeather is not global in node.js.

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