重写toFixed

重写了toFixed

Number.prototype.toFixed = function(c){
    var self = this,
         re = Math.round(self * Math.pow(10,c)) / Math.pow(10,c) + "";
     if( c==0 ) return re;    
     (re.indexOf(".") == -1) && (re += ".");
     var length = re.split(".")[1].length,
         _length = c - length;
     if(_length > 0){
         re +=  Math.pow(10,_length).toString().slice(1);
     }    
     return re ;
}