WebAssembly is great as a target for a low-level code, but in order to do something useful, it needs to interact with the outer world. On the Web, this means performing all sorts of I/O through Web APIs, and here comes the challenge: they are designed to be asynchronous, but WebAssembly is not. Let's take a look at this problem and see how it can be fixed, as well as at some examples we can build by combining power of both modern Web APIs and a fast native compilation target.

1. Asyncifying WebAssembly
Ingvar Stepanyan (@RReverser)
WebAssembly Developer Advocate @ Google

2. Simple WebAssembly

3. Simple WebAssembly

4. WebAssembly with I/O

5. WebAssembly with I/O

6. WebAssembly with I/O

7. WebAssembly with I/O

8. WebAssembly with I/O

9. fread on the Web?
fread
In-memory
storage
localStorage IndexedDB
Network
storage
Native File
System

10. fread on the Web?
fread
In-memory
storage
localStorage IndexedDB
Network
storage
Native File
System

11. Asynchronous Web I/O

12. Asynchronous Web I/O

13. JavaScript event loop

14. JavaScript event loop

15. JavaScript event loop

16. JavaScript event loop

17. JavaScript event loop

18. JavaScript event loop

19. Blocking code

20. Blocking code

21. Blocking code

22. Blocking code

23. WebAssembly with I/O

24. WebAssembly with I/O

25. WebAssembly with I/O

26. WebAssembly with I/O

27. WebAssembly with I/O

29. WebAssembly with async I/O

30. WebAssembly with async I/O

31. WebAssembly with async I/O

32. WebAssembly with async I/O

33. Using Asyncify

34. Using Asyncify

35. Using Asyncify

36. Using Asyncify

37. Using Asyncify

38. Using Asyncify

39. Using Asyncify

40. Using Asyncify

41. Using Asyncify

42. Using Asyncify
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•
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Standalone JavaScript wrapper
https://github.com/GoogleChromeLabs/asyncify
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43. Using Asyncify

45. fread on the Web!
fread
In-memory
storage
localStorage
Network
storage
IndexedDB
Native File
System

46. fread on the Web!
fread
In-memory
storage
localStorage
Network
storage
IndexedDB
Native File
System

47. fread on the Web!
fread
In-memory
storage
localStorage
Network
storage
IndexedDB
Native File
System

48. fread on the Web!
• https://twitter.com/RReverser/status/1221863135881187329

49. libusb on the Web!

50. libusb on the Web!
• https://twitter.com/RReverser/status/1306307329802080256

51. Asyncify downsides

52. Asyncify downsides

53. Future solutions
https://github.com/WebAssembly/design

54. Useful links
• Asyncify announcement post:
https://kripken.github.io/blog/wasm/2019/07/16/asyncify.html
• Asyncify Emscripten docs:
https://emscripten.org/docs/porting/asyncify.html
• Binaryen toolchain: https://github.com/WebAssembly/binaryen
• Standalone Asyncify wrapper:
https://github.com/GoogleChromeLabs/asyncify
• WebAssembly design discussions:
https://github.com/WebAssembly/design