how to solve 'this' problems with node libraries like async and request

libraries, node.js, this

Solution

You're doing it exactly right.

The alternative is to keep a reference to the object always in context instead of using `bind`, but that requires some gymnastics:

Fetcher.prototype.init = function() {
    var self = this;
    async.parallel([
        function(){ return self.getTwitterData() },
        function(){ return self.getKloutData() }
    ], function() {
        console.log('done');
    });
}

Fetcher.prototype.getKloutData = function(callback) {
    var self = this;

    function saveData() {
        // store data
        self.blah();
    }

    request(url, saveData);
};

You can also do the binding beforehand:

Fetcher.prototype.bindAll = function(){
    this.getKloutData = this.prototype.getKloutData.bind(this);
    this.getTwitterData = this.prototype.getTwitterData.bind(this);
};

Fetcher.prototype.init = function(){
    this.bindAll();
    async.parallel([ this.getTwitterData, this.getKloutData ], function() {
        console.log('done');
    });
};

Problem

I've written a node script that gets some data by requesting REST API data (using the library request). It consists of a couple of functions like so: ``` var data = { /* object to store all data */ }, function getKloutData() { request(url, function() { /* store data */} } // and a function for twitter data ``` Because I want to do some stuff after fetching all the I used the library async to run all the fetch functions like so: ``` async.parallel([ getTwitterData, getKloutData ], function() { console.log('done'); }); ``` This all works fine, however I wanted to put everything inside a object pattern so I could fetch multiple accounts at the same time: ``` function Fetcher(name) { this.userID = '' this.user = { /* data */ } this.init(); } Fetcher.prototype.init = function() { async.parallel([ this.getTwitterData, this.getKloutData ], function() { console.log('done'); }); } Fetcher.prototype.getKloutData = function(callback) { request(url, function () { /* store data */ }); }; ``` This doesn't work because async and request change the this context. The only way I could get around it is by binding everything I pass through async and request: ``` Fetcher.prototype.init = function() { async.parallel([ this.getTwitterData.bind(this), this.getKloutData.bind(this) ], function() { console.log('done'); }); } Fetcher.prototype.getKloutData = function(callback) { function saveData() { /* store data */ } request(url, saveData.bind(this); }; ``` Am I doing something basic wrong or something? I think reverting to the script and forking it to child_processes creates to much overhead.

Original source