on type safety in LangChain TS

snippet-8.ts

async safeCallTool(action: AgentAction): Promise<AgentStep> {
  const tool =
    action.tool === "_Exception"
      ? new ExceptionTool()
      : toolsByName[action.tool?.toLowerCase()];
  let observation;
  try {
    observation = tool
      ? await tool.call(action.toolInput)
      : `${action.tool} is not a valid tool, try another one.`;
  } catch (e) {
    if (e instanceof ToolInputParsingException) {
      if (this.handleParsingErrors === true) {
        observation = "Invalid or incomplete tool input. Please try again.";
      } else if (typeof this.handleParsingErrors === "string") {
        observation = this.handleParsingErrors;
      } else if (typeof this.handleParsingErrors === "function") {
        observation = this.handleParsingErrors(e);
      } else {
        throw e;
      }
      observation = await new ExceptionTool().call(
        observation,
        runManager?.getChild()
      );
      return { action, observation: observation ?? "" };
    }
  }

  return { action, observation: observation ?? "" };
}