Javascript Data Structure Range of Integers

var Range = function(lower, upper) {
  if(lower !== Number(lower)) {
    throw new Error("Non-numeric lower bound");
  }//from  www  . ja v a  2s  .  c  om
  if(upper !== Number(upper)) {
    throw new Error("Non-numeric upper bound");
  }
  if(lower > upper) {
    throw new Error("Disordered range");
  }
  if(lower === upper) {
    throw new Error("Empty range");
  }
  this.lower = lower;
  this.upper = upper;
};
Range.prototype.contains = function(other) {
  return this.lower <= other.lower && other.upper <= this.upper;
};
Range.prototype.cardinality = function() {
  return this.upper - this.lower;
};
Range.prototype.create = function(lower, upper) {
  if(lower !== Number(lower)) {
    throw new Error("Lower bound is not a number");
  }
  if(upper !== Number(upper)) {
    throw new Error("Upper bound is not a number");
  }
  if(upper <= lower) {
    throw new Error("Disordered range");
  }
};
Range.prototype.compare = function(other) {
  return (this.lower - other.lower) || (this.upper - other.upper);
};
Range.prototype.overlaps = function(other) {
  return !(this.lower > other.upper || this.upper < other.lower);
};
Range.prototype.equals = function(other) {
  return this.lower === other.lower && this.upper === other.upper;
};
Range.prototype.intersection = function(other) {
  // 1 or 0 ranges
  if(this.overlaps(other)) {
    return [
      new Range(
        Math.max(this.lower, other.lower),
        Math.min(this.upper, other.upper)
      )
    ];
  }
  return [];
};
Range.prototype.union = function(other) {
  // 1 or 2 ranges
  if(this.overlaps(other)) {
    return [new Range(
      Math.min(this.lower, other.lower),
      Math.max(this.upper, other.upper)
    )];
  }
  return [this, other];
};
Range.prototype.difference = function(other) {
  // 0, 1 or 2 ranges
  var result = [];
  if(this.lower < other.lower) {
    result.push(new Range(
      this.lower,
      Math.min(this.upper, other.lower)
    ));
  }
  if(this.upper > other.upper) {
    result.push(new Range(
      Math.max(this.lower, other.upper),
      this.upper
    ));
  }
  return result;
};


console.log(new Range(0, 2).overlaps(new Range(1, 3)));
console.log(new Range(1, 3).overlaps(new Range(0, 2)));
console.log(new Range(0, 2).union(new Range(1, 3))[0].equals(new Range(0, 3)));
console.log(new Range(1, 3).union(new Range(0, 2))[0].equals(new Range(0, 3)));
console.log(new Range(0, 2).union(new Range(2, 3))[0].equals(new Range(0, 3)));
console.log(new Range(2, 3).union(new Range(0, 2))[0].equals(new Range(0, 3)));
console.log(new Range(0, 1).cardinality() === 1);
console.log(new Range(0, 2).cardinality() === 2);
console.log(new Range(0, 11).cardinality() === 11);
console.log("---");