Typescript -> a dynamic response from an API how to type

user_4756106 0
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I am consuming an api that returns nested json. It is dynamic so the keys will often be different, but can only be an object or a string, cannot be an array or number etc.

Here is an example:

const response = {
  name: 'Pete',
  location: 'London',
  age: {
    year: '21'
  }
}

I have tried type it like this:

type Response = {
    [key: string]: string
}

Then in a React component I want to use it like this:

type Response = {
    [key: string]: string
}

const Foo = ({ data }: Response) => {
   return <pre>{JSON.stringify(data, null, 2)}</pre>
}

This gives me the following error:

Property 'x' does not exist on type 'string'

Can anyone point me in the right direction here?

here is a link to stackblitz - https://stackblitz.com/edit/react-ts-4n7vcy?file=App.tsx

typescript ecmascript-6 javascript
2 Answers

What you are doing is assigning the type Response to the props argument of your Foo functional component. So actually, the Foo component accepts a props object with the type of Response, but the data variable is inferred as a string by typescript. What you should do instead is;

interface IFooProps{
  data: Response;
}

const Foo = (props: IFooProps) => {
  return <pre>{JSON.stringify(props.data, null, 2)}</pre>;
};
user_107215630

The issue is that the values in your type are strings. When you extracted the data key its type was a string. You either need to type it like:

type Response = {
  data: {
    [key: string]: string
  }
}

Or accept it in the component like

const Foo = (data: Response) => {
  // ...
}

If you want the values to be either string or nested objects, you can do:

type Response = {
  [key: string]: string | Response
}

And then the data in your example will be of type string | Response.

user_70970450
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