How to get object string index name?

[kemper0110]

Is your feature request related to a problem? Please describe.

Firstly, devcontainer to test a problem.
https://codesandbox.io/p/sandbox/wpkrx7

I struggled how to get name of string index of object type.
For example, for this type I want to extract projectId identifier.

type ProjectJobTypePeriodVal = {
    [projectId: string]: { 
        name: string
        duration: string
    }
}

By debugging and search in sources I came to this solution

const indexType = type.getStringIndexType(); // expect this not undefined

const keyName = type.compilerType.checker
  .getIndexInfosOfType(type.compilerType)[0]
  .declaration.locals.keys()
  .next().value;
// finally keyname is `projectId`

Describe the solution you'd like

I am expecting my solution is bad. Maybe I missed a proper function or approach?

Describe alternatives you've considered

My alternative described above.