A wrapper to deal with floating point numbers in JavaScript. It does a rough conversion to a fraction and then does the operation. The toDecimal method returns the number back as a decimal. For larger numbers use a bigNumber library

floating_point.js

function F(d) {
    if(!(this instanceof F))
        return new F(d);
    
    if(Array.isArray(d))
        this.fraction = d;
    else
        this.fraction = this.convert(d);
}

F.prototype.convert = function(d) {
    var p = d.toString().split('.');
    var n = p[1];
    //if there's no decimal part then we're done
    if(!n)
        return [d, 1];
    var k = Math.pow(10, n.length);
    //return the scaled version
    return [Math.floor(k*d), k];
};

F.prototype.add = function(f) {
    if(!this.isF(f))
        f = new F(f);
    return new F([f.fraction[1]*this.fraction[0]+this.fraction[1]*f.fraction[0], 
        this.fraction[1]*f.fraction[1]]);
};
//Alias
F.prototype.plus = F.prototype.add;

F.prototype.subtract = function(f) {
    if(!this.isF(f))
        f = new F(f);
    return new F([f.fraction[1]*this.fraction[0]-this.fraction[1]*f.fraction[0], 
        this.fraction[1]*f.fraction[1]]);
};
//Alias
F.prototype.minus = F.prototype.subtract;

F.prototype.multiply = function(f) {
    if(!this.isF(f))
        f = new F(f);
    return new F([this.fraction[0]*f.fraction[0], this.fraction[1]*f.fraction[1]]);
};
//Alias
F.prototype.times = F.prototype.multiply;

F.prototype.divide = function(f) {
    if(!this.isF(f))
        f = new F(f);
    return new F([this.fraction[0]*f.fraction[1], this.fraction[1]*f.fraction[0]]);
};
//Alias
F.prototype.over = F.prototype.divide;

F.prototype.isF = function(f) {
    return f instanceof F;
};

F.prototype.toDecimal = function() {
    return this.fraction[0]/this.fraction[1];
};

F.prototype.valueOf = function() {
    return this.toDecimal();
};

F.prototype.toString = function() {
    return String(this.toDecimal());
};
//Example:
//var x = new F(0.2).plus(0.1).times(2);
//console.log(x.toDecimal());