Typescript interface for objects with some known and some unknown property names

Question

I have an object where all the keys are string, some of the values are string and the rest are objects in this form:

var object = {     "fixedKey1": "something1",     "fixedKey2": "something2",     "unknownKey1": { 'param1': [1,2,3], 'param2': "some2", 'param3': 'some3'},     "unknownKey2": { 'param1': [1,2,3], 'param2': "some2", 'param3': 'some3'},     "unknownKey3": { 'param1': [1,2,3], 'param2': "some2", 'param3': 'some3'},     ...     ... }; 

In this object fixedKey1 and fixedKey2 are the known keys which will be there in that object. unknownKey - value pair can vary from 1-n.

I tried defining the interface of the object as:

interface IfcObject {     [keys: string]: {         param1: number[];         param2: string;          param3: string;   } } 

But this throws the following error:

Variable of type number is not assignable of type object

Which I found out that it is not able to assign this interface to "fixedKey - value" pair.

So, how can I do the type checking of this kind of variables?

Answer 1

It's not exactly what you want, but you can use a union type:

interface IfcObject {     fixedKey1: string     fixedKey2: string     [key: string]: string | {         param1: number[];         param2: string;          param3: string;     } } 

It covers your case. But the unknown properties could be of type string.

Answer 2

export interface IfcObjectValues {     param1: number[];     param2: string;     param3: string;         }  interface MyInterface {   fixedKey1: string,   fixedKey2: number,   [x: string]: IfcObjectValues,  } 

Your code in action, see here.