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Learn TypeScript: The Complete Course for Beginners

Members of the Same Type

Explore how TypeScript requires all members in an interface with a string index signature to share the same type. Understand why unions of types are limited and how implementing interfaces in classes is affected. Learn how intersections can be used as a workaround for type restrictions.

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Same type

The interface defined by members and an index type that uses a string as the key must have all its members to be of type string.

📜Note: the code below throws an error ❌

TypeScript 3.3.4
interface MyStringDictionaryWithMembers {
    [key: string]: string;
    m1: string;
    m2: number; // Won't transpile, must be a string
}

If we correct the previous example to have m2 to be a ...