Limit the field type depending on the value of another field

Consider the following scenario:

type ActionType = 
    'action1' |
    'action2' |
    'action3';

interface Action {
    type: ActionType;
    value?: number | Date;
}

Is there a method in typescript to enforce restrictions on the value type based on the type value?

For instance, if type is either action1 or action2, I would like the value field to only accept values of type number, whereas if type is action3, then value should be of type Date.

Although it may not be feasible, it doesn't hurt to ask.

typescript

Answer №1

If you want to increase your odds of success, consider using discriminated unions:

type Event = {
    category: 'category1' | 'category2';
    level: number;
} | {
    category: 'category3';
    date: Date;
}

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