[javascript] Typescript: No index signature with a parameter of type 'string' was found on type '{ "A": string; }

Solved similar issue by doing this:

export interface IItem extends Record<string, any> {
    itemId: string;
    price: number;
}

const item: IItem = { itemId: 'someId', price: 200 };
const fieldId = 'someid';

// gives you no errors and proper typing
item[fieldId]