Why Should I Avoid Namespaces in TypeScript External Modules?

Dilemma of Namespace Usage in TypeScript External Modules

The Problem:

When attempting to use namespaces in TypeScript external modules, users often encounter confusion due to unexpected behavior. Namely:

• Failure to extend classes across modules (e.g., cannot access 'Animal' in 'dog.ts')
• Inability to combine multiple declarations in the same namespace across modules
• Requirement to specify fully qualified names (e.g., 'b.Living.Things.Plant')

Solution: Shift Focus from Namespaces to Modules

The underlying issue stems from a misconception about the purpose of namespaces in external modules. External modules are self-contained, and their main purpose is organization, not conflict avoidance. Therefore, the use of namespaces within external modules is unnecessary and can lead to confusion.

Analogy: The Cupless Solution

Consider a scenario with multiple cups, each representing a namespace. This setup is inefficient because it adds an unnecessary layer between the user and the desired objects/types. Instead, it's better to organize modules directly without relying on namespaces.

Reasons for Avoiding Namespaces in External Modules:

1. Organization: Modules are already organized through their file system structure.
2. Naming Conflicts: Naming conflicts are not a concern in external modules because each module has its own namespace.

Guidance for Structuring External Modules:

• Export Objects as Close to Top-Level as Possible:

  • Use 'export default' for single classes/functions.
  • Place multiple exports at top-level.
  • Use 'namespace' only when exporting a large number of objects.

Red Flags to Avoid:

• Files that declare 'export module Foo { ... }' without any other top-level declarations.
• Files that have a single export class/function that is not 'export default'.
• Multiple files using the same 'export module Foo { ... }' declaration.

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