Q43: What is Declaration Merging?
Declaration Merging occurs when the TypeScript compiler automatically combines multiple declarations sharing the same name into a single unified type definition.
Supported for: interface definitions, namespace definitions, and merging namespaces into functions or classes.
Interface Declaration Merging
interface User {
name: string;
}
interface User {
age: number;
}
const user: User = { name: "Alice", age: 30 }; // Merged into unified interface!💡 TypeScript merges multiple interface definitions sharing the same identifier in the same scope.
Key Takeaways
- Interfaces automatically merge properties across identical namespace names.