parallelSync.js

function parallelSync(funcs, done) {
    if (typeof workers === 'function') {
        done = workers;
        workers = 1;
    }
    
    var counter = funcs.length;
    var idx = 0;
    var queue = [].concat(funcs);
    var results = [];
    var errCount = 0;

    var next = function() {
        queue.shift()(nextGenerator(idx++));
    };
    
    var nextGenerator = function(idx) {
        return function(err) {
            if (err) {
                errCount++;
            }

            results[idx] = [].slice.call(arguments);

            if (--counter === 0) {
                done(errCount ? true : undefined, results);
            } else if (queue.length) {
                next();
            }
        };
    };

    while (workers-- && queue.length) {
        next();
    }
}

parallelSyncExample.js

function over(err, results) {
    if (err) { console.log('there was an error'); }
    
    var errors = results.filter(function(res){
        return res[0];
    }).map(function(res){
        return res[0];
    });
    
    console.log('there are %d errors', errors.length);
    console.log(errors);
    
    console.log(results);
}

// list of tasks
var a = function(done) {
    console.log('start', 'a');
    setTimeout(function(){ done(undefined, 'a'); }, 200);
};
var b = function(done) {
    console.log('start', 'b');
    setTimeout(function(){ done('sadgsd'); }, 500);
};
var c = function(done) {
    console.log('start', 'c');
    setTimeout(function(){ done(undefined, 'c'); }, 100);
};
var d = function(done) {
    console.log('start', 'd');
    setTimeout(function(){ done(undefined, 'd'); }, 1100);
};
var e = function(done) {
    console.log('start', 'e');
    setTimeout(function(){ done('e error'); }, 100);
};

// call parallel with 3 workers
parallelSync([a,b,c,d,e], 3, over);