why am I getting Object literal may only specify known properties AND Element implicitly has an &#03-CodePudding

I must not be understanding how type syntax actually works in typescript... I have the following class:

class MyService {
  static _current_state = 'FOO';

  private static readonly STATE_MAPPING: { [ string: number ] : number } = {
    'FOO': 123,
    'BAR': 456,
  };

  static get STATE () : string {
    return MyService._current_state;
  }

  ...etc

  private isValidThreshold (value: number) : boolean {
    return MyService.STATE_MAPPING[LogService.STATE] >= value;
  }

  ...etc

I get error TS2322: Object literal may only specify known properties, and ''FOO'' does not exist in type '{ [string: number]: number; }'.

and error TS7015: Element implicitly has an 'any' type because index expression is not of type 'number'.

What am I doing wrong?

CodePudding user response：

TS clearly states that you don't have FOO prop in STATE_MAPPING and it has only indexer with a number as a key and FOO is definitely not a number.

class MyService {
  static _current_state = 'FOO';

  private static readonly STATE_MAPPING: { [ index: string ] : number } = {
    'FOO': 123,
    'BAR': 456,
  };

  static get STATE () : string {
    return MyService._current_state;
  }
}

You can play with it here