const set = new Set();

  for (let i = 0; i < 10000; ++i) {

    set.add(`key_${i}`);

  }

​

  for (let j = 0; j < 10000; ++j) {

    set.add(`key_${j}`);

  }

​

  let result = 0;

  for (let k = 0; k < 20000; ++k) {

    result += set.has(`key_${k}`);

  }

​

console.log(result);

​

  const obj = {};

  for (let i = 0; i < 10000; ++i) {

    obj[`key_${i}`] = true;

  }

​

  for (let j = 0; j < 10000; ++j) {

    obj[`key_${j}`] = 1;

  }

​

  let result = 0;

  for (let k = 0; k < 20000; ++k) {

    result += obj.hasOwnProperty(`key_${k}`);

  }

​

console.log(result);

​

  const map = new Map();

  for (let i = 0; i < 10000; ++i) {

    map.set(`key_${i}`, true);

  }

​

  for (let j = 0; j < 10000; ++j) {

    map.set(`key_${j}`, 1);

  }

​

  let result = 0;

  for (let k = 0; k < 20000; ++k) {

    result += map.get(`key_${k}`);

  }

​

console.log(result);

​