Function to generate a percentage calculator.

percentages.js

// Function to generate a percentage calculator.
// Percentages will be rounded to nearest whole number.
// The calculator ensures the entire set of percentages adds up to 100.
var percentageCalculatorGenerator = function(numDataPoints, total) {

    // Ensure cumulative total adds up to 100
    var cumulativeTotal = 0;
    
    // Return the generated function
    return function(value, idx) {
        if (idx + 1 === numDataPoints) {
            // Last data point, just make the whole set adds up to 100
            return 100 - cumulativeTotal;
        } else {
            // Calculate the actual percentage for other data points 
            var pc = Math.round(value / total * 100);
            
            // Record the cumulative total
            cumulativeTotal += pc;
            
            // Return the percentage
            return pc;
        }
    };

};