TS2551: Property XXX does not exist on type

[PatrykKuniczak]

🔎 Search Terms

"property does not exist", "property does not exist under if statement", "property not allowed after if statement excluding it"

🕗 Version & Regression Information

• This changed between versions 5.0.0-beta and 5.9.0-dev.20250318
• This is the behavior in every version I tried, and I reviewed the FAQ for entries about my problem

⏯ Playground Link

https://www.typescriptlang.org/play/?ts=5.9.0-dev.20250318#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-nGLlNgAQighhfZkgEDN8B0IZtzwUh8GIAAtK9iG-Yh8EPNBpivaYhn6IYMDgI8hnKBhhBYKB-DAdo5Aqbh6hYQI2SHBh10-b9L23XdqXgrcUQQFFyi6EATWyTwQHeA5EFQTBcAIEhSC0McG1WUIvg6OR12IGB8AwDATyGBBXjQfophgGDygKUcCxzLEAEIpyfZhthfWUly+ajVy4ni+IEoT0GwPAiDISTjInWTylIhTjFPDigpgAABKQJXVAlouEYRNRwngnKKFzBOQdzRK8iSpJMlh-JqeTmggbjUv4g44iQCj8JYNJOAAEmoXKJwqOIvnaCpwzjeQExYbtexsxd+1aIA

💻 Code

Code is very, very simple, let's look on playground

🙁 Actual behavior

TS2551: Property content-runtime does not exist on type

🙂 Expected behavior

Not occur, because of part TS complaining about, not exists on else statement at all.

[nmain]

startsWith doesn't participate in narrowing out of the box. If you want this, you can add it yourself:

declare global {
  interface String {
    startsWith<K extends string>(searchString: K): this is `${K}${string}`
  }
}

This will fix your example.

[PatrykKuniczak]

startsWith doesn't participate in narrowing out of the box. If you want this, you can add it yourself:

declare global { interface String { startsWith<K extends string>(searchString: K): this is ${K}${string} } } This will fix your example.

Thanks, but it looks like overkill, for my problem, i mean that should work with native solution.

Why it doesn't work and have you plan to implement solution for this?

[nmain]

Ahh, I found the original. Duplicate of https://github.com/microsoft/TypeScript/issues/46958; search terms startsWith in:title.

have you plan to implement solution for this?

See https://github.com/microsoft/TypeScript/issues/46958#issuecomment-983054296