How could I run a function after the completion of a for loop in Node.js?

Question

Say if I have a structure in Node.js shown below:

for (i = 0; i < 50; i++) {
    //Doing a for loop.
}

function after_forloop() {
    //Doing a function.
}

after_forloop();

So how could I make sure the after_forloop() function is fired after the forloop is completed?

In case if you want to see what I am actually working on:

var http = require('http');
http.createServer(function (req, res) {
    res.writeHead(200, {'Content-Type': 'text/plain'});
    res.end('Hello World\n');
}).listen(1337, '127.0.0.1');
console.log('Server running at http://127.0.0.1:1337/');

var proxyChecker = require('proxy-checker');
var fs = require('fs');

function get_line(filename, line_no, callback) {
    fs.readFile(filename, function (err, data) {
        if (err) throw err;
        var lines = data.toString('utf-8').split("\n");
        var firstLineBreak = data.toString('utf-8').indexOf("\n");
        var originalText = data.toString('utf-8');
        var newText = originalText.substr(firstLineBreak + 1);
        if(+line_no > lines.length){
            return callback('File end reached without finding line', null);
        }

        callback(null, lines[+line_no], newText);
    });
}


for (i = 0; i < 50; i++) {
    get_line('proxy_full.txt', i, function(err, line, newText){
        fs.appendFile('proxy.txt', line + '\n', function (err) {
            if (err) throw err;         
        });     
        fs.writeFile('proxy_full.txt', newText, function (err) {
            if (err) throw err;
        });
    })
}

after_forloop();

function after_forloop() {
    proxyChecker.checkProxiesFromFile(
        // The path to the file containing proxies
        'proxy.txt',
        {
            // the complete URL to check the proxy
            url: 'http://google.com',   
            // an optional regex to check for the presence of some text on the page
            regex: /.*/
        },
        // Callback function to be called after the check
        function(host, port, ok, statusCode, err) {
            if (ok) {
                console.log(host + ':' + port);
                fs.appendFile('WorkingProxy.txt', host + ':' + port + '\n', function (err) {
                    if (err) throw err;             
                });
            }                   
        }
    );

    setTimeout(function(){
        fs.writeFile('proxy.txt', "", function (err) {
            if (err) throw err;
        });
        console.log('Proxy Check Completed.')
        process.exit(1); 
    }, 5000);
}

Basically I like to allow the node server run 50 test on a list proxy servers at a time (within five seconds). And then the server should save the working proxies to a new file.

Answer 1

Maybe this helps:

var operationsCompleted = 0;
function operation() {
    ++operationsCompleted;
    if (operationsCompleted === 100) after_forloop(); 
}
for (var i = 0; i < 50; i++) {
    get_line('proxy_full.txt', i, function(err, line, newText){
        fs.appendFile('proxy.txt', line + '\n', function (err) {
            if (err) throw err;
            operation();
        });     
        fs.writeFile('proxy_full.txt', newText, function (err) {
            if (err) throw err;
            operation();
        });
    })
}

Admittedly this isn't an elegant solution. If you're doing a whole lot of this you might want to check out something like Async.js.