JS Async Function Queue

async-function-queue.js

function f1(next) {                
    setTimeout(function() {
        console.log("1");                    
        next.dequeue();                                        
    }, 500);
}

function f2(next) {
    setTimeout(function() {
        console.log("2");                    
        next.dequeue();                    
    }, 1000);
}

function f3(next) {
    console.log("3");                    
    next.dequeue();                    
}

function f4(next) {
    setTimeout(function() {
        console.log("4");                    
        next.dequeue();                                        
    }, 5000);                
}  

function f5(next) {
    setTimeout(function() {
        console.log("5");                                                      
        next.dequeue();
    }, 700);                
}


window.AsyncFunctionQueue = function (onsuccess, onerror) {                

    var q = [];  
    var qstate = "STOPPED";
    var completed = function () {                                        
        onsuccess();
        qstate = "STOPPED";
    }

    this.enqueue = function(f) {                                                                                
        var qlen = q.length;
        var i = {
            f: f,
            dequeue: function() {                            
                var next = (this.next)?this.next:{dequeue:completed, error:onerror}                            
                this.f(next);                            
                q.shift();
            },
            error: function(error) {
                onerror(error);
            }
        };
        q.push(i);        
        if (qlen > 0) {                        
            q[qlen-1].next = i;                        
        }
        return this;
    }

    this.go = function() {
        if (qstate == "STOPPED") {
            qstate= "RUNNING";
            if (q.length > 0) {
                q[0].dequeue();
            } else {
                completed();
            }
        } else {
            throw new Error("Queue already started.");
        }
    }
}    

var q = new AsyncFunctionQueue(function() {console.log("completed!")}, function(error) {console.log(error)});
q.enqueue(f1).enqueue(f2).enqueue(f3).enqueue(f4).enqueue(f5).go();

Yeah, I know Promises. This is an old script from when I just wanted to make my own async function synchronization "API". =P