why getting timezone issue in javascript unix time code example

Example: javascript date timezone

// this example takes 2 seconds to run
const start = Date.now();

console.log('starting timer...');
// expected output: starting timer...

setTimeout(() => {
  const millis = Date.now() - start;

  console.log(`seconds elapsed = ${Math.floor(millis/1000)}`);
  // expected output : seconds elapsed = 2
}, 2000);