he/him 
Type predicates are just an annotation and aren't actually checked. Meaning you can do some pretty wacky and unsafe things. Is there an technical constraint preventing TS from checking these?pic.twitter.com/qtIIzM1Cat
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After using TypeScript there's some features that I'm terrified of that seem counter intuitive. All the following examples produce NO errors and are with every single strict TS option enabled.
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As expressions are another one. The safety guarantees are minuscule. I find the overlapping semantics to be confusing and not actually useful.pic.twitter.com/SqqnJxRz5H
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Refining 'unknown' to an array produces 'Array<any>' where as 'Array<unknown>` would make more sense. Not sure if it does in other places too.pic.twitter.com/gsRa67JFFk
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/terrified/ bud? I think we’re being a bit dramatic
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Your third example is a reasonable concern imo. The other two... not so much.
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I hate TS. But it’s the hype so let’s use it :)
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What is our next best option? Flow? I’m legitimately wondering.
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Typescript is an unsound type checker. I thought that was already the consensus but opening an issue is almost always helpful to the team.
Thanks. Twitter will use this to make your timeline better. UndoUndo
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Here’s a really fun one: function isFeatureXEnabled(): boolean {...} const result = if (isFeatureXEnabled) {...} The underlying semantics of JavaScript naturally make for unsafety everything, not much either TS or Flow can do about that. For safe semantics we need a diff language
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