test.js

const crypto = require('crypto');

const start = Date.now();
crypto.pbkdf2( 'a', 'b', 100000, 512, 'sha512', () => {
  console.log( '1:', Date.now() - start );
});

crypto.pbkdf2( 'a', 'b', 100000, 512, 'sha512', () => {
  console.log( '2:', Date.now() - start );
});

crypto.pbkdf2( 'a', 'b', 100000, 512, 'sha512', () => {
  console.log( '3:', Date.now() - start );
});

crypto.pbkdf2( 'a', 'b', 100000, 512, 'sha512', () => {
  console.log( '4:', Date.now() - start );
});

crypto.pbkdf2( 'a', 'b', 100000, 512, 'sha512', () => {
  console.log( '5:', Date.now() - start );
});

// output
// 3: 2005
// 2: 2007
// 4: 2007
// 1: 2007
// 5: 3004