The left-hand side of an 'in' expression must be a private identifier or of type 'any', 'string', 'number', or 'symbol'

Question

How to fix this type error, even that i already define a String type to key parameter.

function checkIsExistObjectKeys(object: Object, key: String): Boolean {
  return key in object;
}

console.log(
  checkIsExistObjectKeys(
    {
      name: "john",
      lastName: "Francois",
    },
    "name"
  )
);

Answer 1

The key parameter should be of type string , not String .

Answer 2

function checkIsExistObjectKeys(object: Object, key: string): Boolean {
  return Object.keys(object).some(x => x === key);
}