JavascriptでDateを使用して、先史時代の日付を表示するには？

function BigDate(date){
    if(!date){
        this.original = new Date(); 
    }else if(date instanceof BigDate){
        this.original = date.original;
    }else{
        this.original = new Date(date);  
    }
    this.yearBreakpoint = -100000;
    this.breakPoint = Date.UTC(this.yearBreakpoint,0,0).valueOf();
    this.factor = 360000;//needed for our project to make extra space on our axis
}

BigDate.UTC = function (year, month, day, hour, minute, second, millisecond) {
    var temp = new BigDate();
    if(year < -temp.yearBreakpoint){
        temp.setUTCFullYear(year);
        return temp;
    }else{
        temp.original = Date.UTC(year,month,day,hour,minute,second,millisecond);
    }
    return temp.valueOf();
};

BigDate.now = function (){
    var temp = new BigDate();
    temp.original = Date.now();
    return temp.valueOf();
};

BigDate.parse = function (val){
    throw "not implemnted";
};

//custom functions

BigDate.prototype.getUTCDate = function () {
   if(this.valueOf() < this.breakPoint){
       return 0;
   }
   return this.original.getUTCDate();
};
BigDate.prototype.getUTCDay = function () {
   if(this.valueOf() < this.breakPoint){
        return 0;
    }
    return this.original.getUTCDay();
};
BigDate.prototype.getUTCFullYear = function () {
    if(this.valueOf() < this.breakPoint){
        return (this.valueOf() - this.breakPoint) / this.factor;
    }
    return this.original.getUTCFullYear();
};
BigDate.prototype.getUTCHours = function () {
    if(this.valueOf() < this.breakPoint){
        return 0;
    }
    return this.original.getUTCHours();
};
BigDate.prototype.getUTCMilliseconds = function () {
    if(this.valueOf() < this.breakPoint){
        return 0;
    }
    return this.original.getUTCMilliseconds();
};
BigDate.prototype.getUTCMinutes = function () {
    if(this.valueOf() < this.breakPoint){
        return 0;
    }
    return this.original.getUTCMinutes();
};
BigDate.prototype.getUTCMonth = function () {
    if(this.valueOf() < this.breakPoint){
        return 0;
    }
    return this.original.getUTCMonth();
};
BigDate.prototype.getUTCSeconds = function () {
    if(this.valueOf() < this.breakPoint){
        return 0;
    }
    return this.original.getUTCSeconds();
};

BigDate.prototype.setUTCDate = function (val) {
    if(val >= this.yearBreakpoint){
      return this.original.setUTCDate(val);
   }
};
BigDate.prototype.setUTCFullYear = function (val) {
    if(val < this.yearBreakpoint){
        this.original.setTime((parseInt(val) * this.factor) + this.breakPoint);
    }else{
        this.original.setUTCFullYear(val);
    }
    return this.valueOf();
};
BigDate.prototype.setUTCHours = function (val) {
    if(val >= this.yearBreakpoint){
      return this.original.setUTCHours(val);
    }
};
BigDate.prototype.setUTCMilliseconds = function (val) {
    if(val >= this.yearBreakpoint){
      return this.original.setUTCMilliseconds(val);
    }
};
BigDate.prototype.setUTCMinutes = function (val) {
    if(val >= this.yearBreakpoint){
        return this.original.setUTCMinutes(val);
    }
};
BigDate.prototype.setUTCMonth = function (val) {
    if(val >= this.yearBreakpoint){
      return   this.original.setUTCMonth(val);
    }
};
BigDate.prototype.setUTCSeconds = function (val) {
    if(val >= this.yearBreakpoint){
       return  this.original.setUTCSeconds(val);
    }
};

BigDate.prototype.setTime = function (val) {
    this.original.setTime(val);
    return this.valueOf();
};
BigDate.prototype.valueOf = function () {
    return this.original.valueOf();
};


BigDate.prototype.toDateString = function () {
    if(this.valueOf() < this.breakPoint){
        return "Jan 01 " + this.getUTCFullYear();
    }
    return this.original.toDateString();
};
BigDate.prototype.toISOString = function () {
    if(this.valueOf() < this.breakPoint){
        return this.getUTCFullYear() + "-01-01T00:00:00.000Z";
    }
    return this.original.toISOString();
};

BigDate.prototype.toJSON = function () {
    throw "not implemnted";
};
BigDate.prototype.toLocaleDateString = function () {
    throw "not implemnted";
};
BigDate.prototype.toLocaleTimeString = function () {
    throw "not implemnted";
};
BigDate.prototype.toLocaleString = function () {
    throw "not implemnted";
};
BigDate.prototype.toTimeString = function () {
    throw "not implemnted";
};
BigDate.prototype.toUTCString = function () {
    if(this.valueOf() < this.breakPoint){
        return "01 Jan "+ this.getFullYear() +" 00:00:00 GMT";
    }
    return this.original.toUTCString();
};




/**
 * Don't need no timezones
 */

BigDate.prototype.getDate = function () {
    return this.getUTCDate();
};
BigDate.prototype.getDay = function () {
    return this.getUTCDay();
};
BigDate.prototype.getFullYear = function () {
    return this.getUTCFullYear();
};
BigDate.prototype.getHours = function () {
    return this.getUTCHours();
};
BigDate.prototype.getMilliseconds = function() {
    return this.getUTCMilliseconds();
};
BigDate.prototype.getMinutes = function() { 
    return this.getUTCMinutes();
};
BigDate.prototype.getMonth = function () {
    return this.getUTCMonth();
};
BigDate.prototype.getSeconds = function () {
    return this.getUTCSeconds();
};
BigDate.prototype.getTimezoneOffset = function () {
    return 0;
};
BigDate.prototype.getTime = function () {
    return this.valueOf();
};

BigDate.prototype.setDate = function (val) {
    return this.setUTCDate(val);
};
BigDate.prototype.setFullYear = function (val) {
    return this.setUTCFullYear(val);
};
BigDate.prototype.setHours = function (val) {
    return this.setUTCHours(val);
};
BigDate.prototype.setMilliseconds = function (val) {
    return this.setUTCMilliseconds(val);
};
BigDate.prototype.setMinutes = function (val) {
    return this.setUTCMinutes(val);
};
BigDate.prototype.setMonth = function (val) {
    return this.setUTCMonth(val);
};
BigDate.prototype.setSeconds = function (val) {
    return this.setUTCSeconds(val);
};

BigDate.prototype.toString = function () {
    return this.toUTCString();
};