async.js

// defining a function
var async_factorial = function(n, callback){
    console.log("step1");
    var fact = 1;
    process.nextTick(function(){
        for(var i=1; i<n; i++) {
                fact = fact*i;
        }
        console.log("step2");
        callback(fact);
    });
};

// using the function
async_factorial(50, function(result){
    console.log("step3");
    console.log("value is:" + result);
});

console.log("Out of async");