Combination of values in object attributes typescript [duplicate]

Question

I was wondering if there is a construct in typescript that I can use in order to restrict possible values of an object depending on the values. I can describe it something like that:

interface IObject = {
key1:string;
key2:string;
key3:"A" | null;
key4: (if key3 is 'A' then allow 'value1' |'value2' else if it is null then allow "value3" | "value4" 
}

Does typescript support that?

Yes it almost does. The questions are almost similar, but the exact match is below — JmRag
– JmRag, Commented May 16, 2022 at 12:48

Tobias S. · Accepted Answer · 2022-05-16 12:30:27Z

1

You can declare the type like this:

type IObject = {
  key1:string;
  key2:string;
} & ({
  key3:"A",
  key4: 'value1' |'value2'
} | {
  key3: null,
  key4: "value3" | "value4" 
})

We basically create a union of all valid key3 and key4 combinations and intersect them with the rest of the properties.

answered May 16, 2022 at 12:30

Tobias S.

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