Design Bitset.js

var Bitset = function(size) {
    //this.bits = new Array(size).fill(0);
    //this.bitsOp = new Array(size).fill(1);
    this.set0 = new Set();
    this.set1 = new Set();
    for (let i = 0; i<size; i++) this.set0.add(i);
};

/** 
 * @param {number} idx
 * @return {void}
 */
Bitset.prototype.fix = function(idx) {
  //this.bits[idx] = 1;
  //this.bitsOp[idx] = 0;
  if (this.set0.has(idx)) {
    this.set1.add(idx);
    this.set0.delete(idx);
  }
};

/** 
 * @param {number} idx
 * @return {void}
 */
Bitset.prototype.unfix = function(idx) {
  //this.bits[idx] = 0;
  //this.bitsOp[idx] = 1;
  if (this.set1.has(idx)) {
    this.set0.add(idx);
    this.set1.delete(idx);
  }
};

/**
 * @return {void}
 */
Bitset.prototype.flip = function() {
  //this.bits = this.bits.map(x=>(x)?0:1); 
  //this.bits.forEach(x=>x=(x)?0:1); 
  [this.set0, this.set1] = [this.set1, this.set0];
};

/**
 * @return {boolean}
 */
Bitset.prototype.all = function() {
  //return (this.bits.filter(x=>x).length == this.bits.length) 
  //return !this.bits.includes(0);
  //for (let i = 0; i<this.bits.length; i++)
    //if (this.bits[i] === 0) return false;
   //return true; 
  return this.set0.size===0
};

/**
 * @return {boolean}
 */
Bitset.prototype.one = function() {
    //return this.bits.filter(x=>x).length>0 
    //return this.bits.includes(1);
    //for (let i = 0; i<this.bits.length; i++)
      //if (this.bits[i] === 1) return true;
     //return false; 
  return this.set1.size>0;
};

/**
 * @return {number}
 */
Bitset.prototype.count = function() {
    //return this.bits.filter(x=>x).length 
  //return this.bits.reduce((sum, cur)=>sum+cur);
  return this.set1.size;
};

/**
 * @return {string}
 */
Bitset.prototype.toString = function() {
    //return this.bits.join('');
  let set = new Array(this.set0.size+this.set1.size);
  for (let i=0; i<set.length; i++) {
    set[i] = this.set0.has(i)?0:1;
  }
  return set.join('');
};