Creating a Typescript interface with at least one specified type

I've recently delved into using typescript. Currently, I'm faced with a scenario where I need to import available types from backend endpoints. In one specific instance, an endpoint can support two types as parameters.

Example: 

interface B extends A {
    value?: string,
    values?: string[]
}

Here, A represents the type imported from the backend, and it may have either value: string or values: string[].

Currently, I've made both properties optional in the interface B, but I believe this is not the ideal solution. How can I structure interface B so that it only contains either value or values?

Thank you.

typescript

Answer №1

If you're searching for the solution to the "either or" scenario, you'll need a concept known as a union type. These are created using the pipe | operator and signify "either this type OR that type".

Here's an illustration:

type StringOrNumber = string | number;

Alternatively:

type FooOrBar = { foo: string; } | { bar: string; };

For your specific situation:

interface IWithValue {
   value: string;
}

interface IWithValues {
   values: string[];
}

type IValueOrValues = IWithValue | IWithValues;

You can experiment with an example in the typescript playground.

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