Javascript Number simEq(number, digits)

DEFAULT_DIGIT = 5;/*  ww w  . j a va 2s. c o  m*/
Number.prototype.simEq = function(number, digits) {
 digits = digits == undefined ? DEFAULT_DIGIT : digits;
 var n1 = this.toFixed(digits);
 var n2 = number.toFixed(digits);
 if (n1 == -0)
  n1 = 0;
 if (n2 == -0)
  n2 = 0;
 return n1 == n2;
}