Funny frontend engineer (React / Vue / TypeScript) Creator of is-kit is-kit.dev/en DSA View View github.com/nyaomaru/dsa-view…
The Netherlands, Heerlen
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unknown type is unknown.
So, if you want to use correctly, you should do type narrowing.
Then, you can use is-kit.
github.com/nyaomaru/is-kit
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A type guard can prove two things at runtime:
1. this node is a CallExpression
2. its expression is an Identifier
But once you extract that check into a reusable function, will TypeScript preserve both facts?
That question sent me down a rabbit hole. 😸
#TypeScript #WebDev
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A stale type guard can fail in two ways:
❌ Reject valid data → loud bug
⚠️ Accept invalid data → silent bug
The second one is scarier because the failure happens much later, far from the real cause.
That’s the drift I wrote about here:
dev.to/nyaomaru/your-type-gu…
#TypeScript
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New article! 🔧
A TypeScript type guard can keep compiling after its runtime checks drift from the type.
value is User is a promise, not proof.
Here’s how typedStruct<User>() catches that drift at compile time. 👀
dev.to/nyaomaru/your-type-gu…
#TypeScript #OpenSource
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A hand-written type guard can be perfectly valid TypeScript and still be stale at runtime.
That’s the problem I’ve been exploring this week.
Tomorrow I’ll publish the full write-up on keeping runtime guards in sync with existing TypeScript types. 🔧
#TypeScript #OpenSource
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nyaomaru retweeted
We’ve added is-kit project by @nyaomaru_dev to the EmbedCatalog.
About:
Build small guards. Compose them. Lightweight, zero-dependency TypeScript type guards for runtime validation and natural narrowing.
Link in the comments.
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Optional and nullable are two different contracts. 👀
nickname?: string | null
means:
- the key may be missing
- if present, the value may be `null`
Those are separate runtime decisions too.
`optionalKey(nullable(isString))`
#TypeScript
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What if TypeScript could catch that type-guard drift for you?
With `typedStruct<User>()`, the existing type becomes a compile-time contract for the guard definition.
Missing field? Error.
Wrong guard? Error.
Runtime checks stay explicit. 👀
#TypeScript #OpenSource
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Yesterday: a type predicate is a promise, not proof.
Here’s where that becomes dangerous 👀
Add a new field to `User`, forget to update `isUser`
and TypeScript can still compile.
The type changed.
The runtime guard didn’t.
#TypeScript #JavaScript
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TypeScript type guard finding 👀
A return type like:
`value is User`
is a promise made by the function. not proof that the runtime implementation actually checks every field.
That gap can quietly become a maintenance problem.
#TypeScript #JavaScript
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There’s a TypeScript side to `filter(Boolean)` too.
It removes falsy values at runtime, but `Boolean` isn’t a type guard.
So TypeScript doesn’t generally know that `null` and `undefined` are gone.
More in my latest article 👇
dev.to/nyaomaru/why-filterbo…
#TypeScript #JavaScript
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New article! 😸
filter(Boolean) is convenient, but it’s not a nullish filter.
Valid values like 0, false, and "" can disappear too.
Falsy ≠ Nullish.
dev.to/nyaomaru/why-filterbo…
#TypeScript #JavaScript #OpenSource
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My post was featured in DEV Community’s Top 7 Posts of the Week! 😸🎉
Really happy to see it picked up by the DEV team.
Thanks to everyone who read, reacted, and commented! ❤️🔥
dev.to/devteam/top-7-feature…
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Tiny JavaScript edge case 👀
`value != null` is often used as a short nullish check.
But `document.all` is a historical browser exception: it behaves as nullish under loose equality.
JavaScript is fun. 😹
#JavaScript #WebDev
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Not every check needs a library. 😸
If you only need to remove `null` and `undefined` once, an inline type predicate is perfectly fine.
Reusable guards make more sense when the same meaning starts repeating.
github.com/nyaomaru/is-kit
#TypeScript #OpenSource
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There’s a TypeScript difference too 👀
`filter(Boolean)` removes falsy values at runtime, but `Boolean` isn’t a type guard.
So TypeScript doesn’t generally know that `null` and `undefined` are gone.
#TypeScript #JavaScript
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Small JavaScript reminder 👀
`filter(Boolean)` doesn’t mean “remove null and undefined.”
It means “keep only truthy values.”
So `0`, `false`, and `""` disappear too.
Falsy and missing are different requirements.
#JavaScript #TypeScript
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The code itself is often not the hardest part of DSA.
It’s keeping track of what changes while it runs. 👀
- `left` moved.
-`water` increased.
-A bucket changed.
That’s what I want to see with DSA View View. 😸
dev.to/nyaomaru/learn-trappi…
#DSA #TypeScript #OpenSource
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New DSA View View article! 👀👀
🌧️ Trapping Rain Water → Two Pointers
🔢 Top K Frequent → Buckets
👉 Selection Sort → Selection
Watch the runtime state change step by step. 😸
dev.to/nyaomaru/learn-trappi…
#DSA #TypeScript #OpenSource
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is-kit v1.14.1 is out 😸
This release fixes two non-obvious runtime paths
• preserves strict nullish semantics in browsers, including the document.all edge case
• removes exception-driven checks from the successful isTypedArray path
github.com/nyaomaru/is-kit/r…
#OpenSource
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Thought I’d found a TypeScript Compiler API gap.
Then I reproduced it with plain objects. 👀
So it’s not AST-specific, it’s a generic property-refinement composition problem.
is-kit keeps the parent + child refinement reusable without a manual return.
#TypeScript #OpenSource
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