Is there a difference between type and interface in TypeScript?

In TypeScript, type and interface have similarities, but there are key differences:

• Extensibility:

  • interface can be extended (extends) and augmented (declaration merging).
  • type cannot be augmented after declaration, but new types can be created based on existing ones through unions and intersections.

• Capabilities:

  • type can describe not only objects but also primitives, unions, tuples, etc.
  • interface is only meant for describing object and class structures.

• Usage:

  • interface is often preferred for describing public APIs and objects, as it supports declarative extension.
  • type is convenient for complex types, unions, and aliases.

Example:

interface User {
  name: string;
}

interface User {
  age: number; // interfaces will merge
}

const user: User = { name: "Alice", age: 30 };

// type does not support merging

type ID = string | number;