This document contains code snippets and graphs demonstrating the difference between synchronous and asynchronous functions in JavaScript. It shows how synchronous functions like crypto.pbkdf2Sync block further code execution, while asynchronous functions like crypto.pbkdf2 and https.request allow other work to continue in parallel and complete faster overall.

7. •
•
•
•
•
•

13. const crypto = require('crypto');
const NUM_REQUESTS = 2;
for (let i = 0; i < NUM_REQUESTS; i++) {
crypto.pbkdf2Sync('secret', 'salt', 10000, 512, 'sha512');
}

14. 0 50 100 150 200 250 300 350 400
Time (milliseconds)
Execution Timeline

15. const crypto = require('crypto');
const NUM_REQUESTS = 2;
for (let i = 0; i < NUM_REQUESTS; i++) {
crypto.pbkdf2('secret', 'salt', 10000, 512, 'sha512', () => {});
}

16. 0 50 100 150 200 250 300 350 400
Time (milliseconds)
Execution Timeline

17. 0 50 100 150 200 250 300 350 400
Time (milliseconds)
Execution Timeline

18. 0 50 100 150 200 250 300 350 400
Time (milliseconds)
Execution Timeline

19. 0 50 100 150 200 250 300 350 400
Time (milliseconds)
Execution Timeline
2 Requests
4 Requests
6 Requests

22. const https = require('https');
const NUM_REQUESTS = 2;
for (let i = 0; i < NUM_REQUESTS; ++i) {
https.request('https://nebri.us/static/me.jpg', (res) => {
res.on('data', () => {});
res.on('end', () => {});
}).end();
}

23. 0 100 200 300 400 500 600 700 800
Time (milliseconds)
Execution Timeline

24. 0 100 200 300 400 500 600 700 800
Time (milliseconds)
Execution Timeline

25. 0 100 200 300 400 500 600 700 800
Time (milliseconds)
Execution Timeline

29. •
•
•
•
•
•
•
•
•
•
•
•
•

30. Bryan Hughes, @nebrius