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Comment by topaxi | Hacker News Reader

xstate is a nice javascript library which even generates charts out of your defined states in your app: https://github.com/davidkpiano/xstate

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Similarly, I have a early-stage JS library for hierarchical statecharts. It revolves around nested contexts and an explicit message passing interface for controlling states between parent/child/sibling. Example:

https://github.com/jdque/royal/blob/master/test.js

off-topic but why do you use 'let' instead of 'const'? In royal.ts you do that all the time even though you variables don't change! Is there a reason for that?

I have no idea why they did it, but I have argued for quite some time that const has very little practical value, because its effect is always lexical and local.

To demonstrate that this is so, I suggest that we can write a processor that converts all lets to consts where possible. I also demonstrate that this is so by asking, "What bug will const catch that our tests will not catch?"

_Immutable Data_, on the other hand, is marvellous. Immutability has nonlocal effects, and it is not something that can be trivially verified.

I agree with your assessment, but for me it is a message from the programmer to the reader. Hey this value will not be re-assigned during the following scope block. If I see a let, I know I must be careful. Of course this doesn't apply to properties of objects ... which is a pity!

Thanks! I have some awesome updates to announce very soon!

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