'string | number' is not allowed as an index signature parameter type

[malibuzios]

TypeScript Version:
1.8.7

Code

type StringOrNumberKeys: { [key: string | number]: number };

Expected behavior:
Should work

Actual behavior:

Error: an index signature parameter must be 'string' or 'number'

[mhegazy]

duplicate of #1705

[mhegazy]

also note, that using string indexer will achieve what you want.

type StringOrNumberKeys: { [key: string]: number };