Puzzle test

Readme.md

Put both files in the same directory and run 'node app'

app.js

var throttler = require('./throttler');

var asyncFunction = function(x, callback) {
  return setTimeout((function() {
    return callback(x * x);
  }), 1000);
};

throttledFunction = throttler(asyncFunction, 3);

for (var i = 0; i < 100; i++) {  
    // Call throttledFunction
    throttledFunction(i, function(y) {
      console.log(y);
    });
};

throttler.js

module.exports = function(asyncFunction, concurrencyLevel) {
    var queue = [];
    var running = 0;

    var throttledFunction = function(x, callback) {
        queue.push(function(done) {
            asyncFunction(x, function(result){
                // call fist done function because A resource is "in use" between the time 
                // the asynchronous function starts and the time it calls its callback with the result.
                done();
                callback(result);
            });
        });
    };

    // Run a function each 1ms (can be changed) to check the data in the queue.
    var intervalID = setInterval(function() {
        if (queue.length > 0 && running < concurrencyLevel) {
            running++;

            // dequeue and run the function.
            var func = queue.shift();
            func(function(){
                
                running--;    
            });            
        };
    }, 1);

    return throttledFunction;
};