Element implicitly has an 'any' type because type '{}' has no index signature. [7017]

Question

I am using typescript and am seeing the following error

[ts] Element implicitly has an 'any' type because type '{}' has no index signature. [7017]

const store = {};
setItem: jest.fn((key, value) => {
    store[key] = value.toString();
})

I can fix it by setting the store to any like so

const store: any = {};

but I would like to type it, but can't figure out how to do this. Can anyone help?

Answer 1

Well, what kind of type do you want it to have? If it's just a simple key-value pair then this will suffice:

type Dict = { [key: string]: string };

const store: Dict = {};

store['foo'] = 'bar';

Edit (June of 2019)

Typescript also has a built-in type called Record which is meant for this use case - as long as your type is not supposed to have any predefined keys!

const store: Record<string, string> = {};

store.foo = 'bar';