typescript에서 enum에 string을 인덱스로 썼을 때 발생하는 문제 해결

 

https://stackoverflow.com/questions/57086672/element-implicitly-has-an-any-type-because-expression-of-type-string-cant-b

Element implicitly has an 'any' type because expression of type 'string' can't be used to index

// bad
const _getKeyValue = (key: string) => (obj: object) => obj[key];

// better
const _getKeyValue_ = (key: string) => (obj: Record<string, any>) => obj[key];

// best
const getKeyValue = <T extends object, U extends keyof T>(key: U) => (obj: T) =>
  obj[key];

Bad - the reason for the error is the object type is just an empty object by default. Therefore it isn't possible to use a string type to index {}.

 

Better - the reason the error disappears is because now we are telling the compiler the obj argument will be a collection of string/value (string/any) pairs. However, we are using the any type, so we can do better.

 

Best - T extends empty object. U extends the keys of T. Therefore U will always exist on T, therefore it can be used as a look up value.

 

https://www.angularjswiki.com/angular/how-to-convert-a-string-to-enum-in-typescript-or-angular/

How To Convert a string to Enum in Typescript/Angular | Angular Wiki

다음 글을 참고하여 해결하였다.

 

원래 코드

// Change string to LegalPersonNameTypeCode
export function toLegalPersonNameTypeCode(legalPersonNameIdentifierType: string) {
  if (LegalPersonNameTypeCode[legalPersonNameIdentifierType]) {
    return LegalPersonNameTypeCode[legalPersonNameIdentifierType];
  }
  throw new Error(`${legalPersonNameIdentifierType} must be one of 'LEGL','SHRT', 'TRAD' `);
}

 

수정한 코드

// Change string to LegalPersonNameTypeCode
export function toLegalPersonNameTypeCode(legalPersonNameIdentifierTypeParam: string) {
  const legalPersonNameIdentifierType: LegalPersonNameTypeCode = (<any>legalPersonNameIdentifierTypeParam)[
    legalPersonNameIdentifierTypeParam
  ];

  if (legalPersonNameIdentifierType) {
    return legalPersonNameIdentifierType;
  }
  throw new Error(`${legalPersonNameIdentifierType} must be one of 'LEGL','SHRT', 'TRAD' `);
}

타입을 단순하게 string으로만 지정해 주는 것이 아니라 더 자세히 지정해 주어야 오류가 나지 않는다.