Explicitly typing an object with TypeScript

Question

I\'m working on converting my little library from JavaScript to TypeScript, and I have a function there

function create(declarations: Declarations) {
         


        

Answer 1

It seems this is not possible to do, in the TypeScript Deep Dive book there's a section on exactly this. Although you can declare a type you can't actually create an object with it in TS:

// No error on this type declaration:
type Declarations = {
    [key: string]: string;
} & {
    onMember: number;
    onCollection: number;
}

// Error does appear here indicating type `number` is not assignable to type `string`.
const declarations: Declarations = {
    onMember: 0,
    onCollection: 0,
    other: 'Is a string'
}

TypeScript Playground link.