Classes

Basic classes

Use classes as you normally would:

class Counter {
  private value = 0

  next() {
    this.value += 1
    return this.value
  }
}

Construct instances with new and keep initialization in the constructor or field declarations.

Fields and methods

Public and private fields are intended for normal application code:

class TokenStore {
  #tokens = new Map<string, string>()

  set(id: string, token: string) {
    this.#tokens.set(id, token)
  }
}

Prefer methods over assigning new function properties to instances at runtime.

Inheritance

Simple inheritance is supported:

class ApiError extends Error {
  constructor(public status: number, message: string) {
    super(message)
  }
}

Keep inheritance shallow. Composition is usually easier to test and easier for compatibility checks.

Recommendations

• Avoid modifying prototypes at runtime.
• Prefer constructor arguments over global state.
• Keep class fields explicit.
• Test subclasses at the public method level.