220105-ts-key.ts

const foo = [
  { key: 'one' },
  { key: 'two' },
];

const bar = {
  one: 'one',
  two: 'two',
};

foo.forEach((item) => {
  // Element implicitly has an 'any' type because expression of type
  // 'string' can't be used to index type '{ one: string; two: string; }'.
  // No index signature with a parameter of type 'string' was found one
  // type '{ one: string; two: string }' 
  console.log(bar[item.key]);
});