0c. Optional Properties & Parameters

The ? after a property or parameter name means it can be undefined (or omitted entirely).

Optional interface properties:

File: packages/coding-agent/src/modes/rpc/rpc-client.ts L26-34

export interface RpcClientOptions {
  cliPath?: string; // can be omitted -- defaults handled in code
  cwd?: string;
  env?: Record<string, string>;
  provider?: string;
  model?: string;
  args?: string[];
}

Every field is optional. You can call new RpcClient({}) or new RpcClient({ cwd: "/tmp" }).

Optional function parameters:

File: packages/mom/src/tools/bash.ts L35-38

execute: async (
  _toolCallId: string,
  { command, timeout }: { label: string; command: string; timeout?: number },
  signal?: AbortSignal,
) => { ... }

timeout?: number means timeout can be a number or undefined. signal?: AbortSignal can be omitted entirely.

Difference from JS: In JavaScript, all parameters are implicitly optional. In TypeScript, required parameters must be passed or you get a compile error.