Using Array.reduce to pipeline functions

pipeline.js

var Pipeline = function (series, initialInput) {
   this.series = series;
   this.initial = function () {
     return initialInput;
   };
   this.hasPerformed = false;
};

Pipeline.prototype.addFunction = function (fn, index) {
   if (index === undefined) {
     this.series.push(fn);
   } else {
     this.series.splice(index, 0, fn);
   }
};

Pipeline.prototype.perform = function () {
    var reducer = function (previousValue, currentValue) {
     // invoke the previous function in the series to get the result;
     var inputForNext = previousValue();

     // bind the input to current function
     return currentValue.bind(null, inputForNext);
   };
   
   this.finalResult = this.series.reduce(reducer, this.initial)();
   this.hasPerformed = true;
};

Pipeline.prototype.getResult = function () {
   if (this.hasPerformed) {
     return this.finalResult;
   } else {
     this.perform();
     return this.finalResult;
   }
};


// this is how the implementation works
// pass the initial value as the second argument
// say the price of the good is 100

var series = [tax, serviceTax];

var pipeline = new Pipeline(series, 100);

pipeline.addFunction(formatMoney);

// get the final value
var result = pipeline.getResult();