Not quite sure what I'm missing here

[amritk]

Hello, this lib looks really cool but I'm not quite sure how to get it to work

  if (startsWith(props.example.type, 'http')) 
    console.log(props.example.type)

the type is not narrowed. I thought maybe because it is nested. But this doesn't work either

  const type = props.example.type  
  if (startsWith(type, 'http')) 
    console.log(type)

What am I missing here?

[gustavoguichard]

Hi @amritk , would you mind sending me a TS playground example so I can better understand your problem and maybe fix a potential bug?

[edit]: If I undestood it right, it is not what you'd expect.
The resulting value of native startsWith is a boolean and in this case it will be true.
Check this example:

The goal of string-ts is to have a consistent result for the common string functions at both runtime and type levels, which is happening in this case.

Unfortunately it won't be enough for the TS compiler to understand the narrowing you expect here. Maybe in future iterations of TS ;)

[amritk]

Oh thats what it does, I thought it would narrow the type as well. Yea it doesn't work in typescript either Playground

[amritk]

I was trying to narrow the type by checking a nested property, actually its unrelated to this lib 😓

[gustavoguichard]

No worries, I'd expect it to work too and with every new version they've been improving the inference algorithm