Problematic Decimal Arithmetic in Javascript

decimal_arithmetic.js

// decimal_arithmetic.js
// From http://www.brewsession.com/problematic-decimal-arithmetic-in-javascript/

String.prototype.digitsAfterDecimal = function()
{  var parts = this.split(".", 2);  // FIXME: Not international!
   if( ! parts[1] )
   {  parts[1] = "";  }
   return parts[1].length;
};

Number.prototype.biggerScalar = function(n)
{  return n.scale() > this.scale() ? n.scale() : this.scale();  };

Number.prototype.digitsAfterDecimal = function()
{  return this.toString().digitsAfterDecimal();  };

Number.prototype.divided = function(n)
{  return this.dividedBy(n);  };

Number.prototype.dividedBy = function(n)
{  return this.multiply( n.reciprocal() );  };

Number.prototype.minus = function(n)
{  return this.plus( n.negative() );  };

Number.prototype.multiply = function(n)
{  var s = this.biggerScalar(n);
   return (Math.round(s*this,0) * Math.round(s*n,0)) / (s*s);
};

Number.prototype.negative = function()
{  return -1 * this;  };

Number.prototype.plus = function(n)
{  var s = this.biggerScalar(n);
   return (Math.round(s*this,0) + Math.round(s*n,0)) / s;
};

Number.prototype.reciprocal = function()
{  return 1 / this;  };

Number.prototype.scale = function()
{  return Math.pow(10, this.digitsAfterDecimal() );  };