Web worker

Multithreading javascript empowers everything.

But, again, this time, we have IE 9 issues.

IE9 doesn't support web worker natively ( IE 10+ supports).

The shim we can find online is just web worker FALLBACK, which means it's not actually multithreading, it's just dumps the code into the main thread carefully, 

therefore serialize all 'threads'  into one single thread.

No performance gain at all, but it does solve the web worker API compatibility issue.