gistfile1.js

// Calculate the average of a number of values as they are produced
var newAverage = function() {
  var o = {};

	var n       = 0; o.n       = function() { return n; }       // How many values we have, 0 before you add one
	var total   = 0; o.total   = function() { return total; }   // The total sum of all the given values
	var minimum = 0; o.minimum = function() { return minimum; } // The smallest value we have seen, 0 before we have any values
	var maximum = 0; o.maximum = function() { return maximum; } // The largest value we have seen, 0 before we have any values
	var recent  = 0; o.recent  = function() { return recent; }  // The most recent value you added, 0 before we have any values

	// Record a new value to make it a part of this average
	o.add = function(value) {
		n++; // Count another value
		total += value; // Add the value to our total
		if (n === 1 || value < minimum) minimum = value; // First or smallest value
		if (n === 1 || value > maximum) maximum = value; // First or largest value
		recent = value; // Remember the most recent value
	},

	// The current average, 0 before we have any values
	o.average = function() {
		if (n === 0) return 0;
		return total / n;
	},

	// The current average in thousandths, given 4, 5, and 6, the average is 5000
	o.averageThousandths = function() { return averageMultiply(1000); },
	// The current average multiplied by the given number
	o.averageMultiply = function(multiply) {
		if (n === 0) return 0;
		return multiply * total / n;
	},

	// Text that describes the current average, like "5.000", "Undefined" before we have any values
	o.say = function() {
		if (n === 0) return 'Undefined';
		return describe.decimal(averageThousandths(), 3);
	};

	return o;
};

var a = newAverage();
a.add(4);
a.add(5);
a.add(6);
console.log(a.say());//5