How to get object string index name?#1572

**Is your feature request related to a problem? Please describe.** Firstly, devcontainer to test a problem. [https://codesandbox.io/p/sandbox/wpkrx7](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. ```ts 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.