# Extending a plug-in

Before you begin, be sure to complete the Installing the sample plug-in tutorial.

# Overview

This tutorial demonstrates how to extend the plug-in that is bundled with this sample by:

  1. Creating a new programmatic API
  2. Creating a new command definition
  3. Creating a new handler

We'll do this by using @zowe/imperative infrastructure to surface REST API data on our Zowe™ CLI plug-in.

Specifically, we're going to show data from this URI (opens new window) by Typicode (opens new window). Typicode serves sample REST JSON data for testing purposes.

At the end of this tutorial, you will be able to use a new command from the Zowe CLI interface: zowe zowe-cli-sample list typicode-todos

Completed source for this tutorial can be found on the typicode-todos branch of the zowe-cli-sample-plugin repository.

# Creating a Typescript interface for the Typicode response data

First, we'll create a Typescript interface to map the response data from a server.

Within zowe-cli-sample-plugin/src/api, create a folder named doc to contain our interface (sometimes referred to as a "document" or "doc"). Within the doc folder, create a file named ITodo.ts.

The ITodo.ts file will contain the following:

export interface ITodo {
    userId: number;
    id: number;
    title: string;
    completed: boolean;

# Creating a programmatic API

Next, we'll create a Node.js API that our command handler uses. This API can also be used in any Node.js application, because these Node.js APIs make use of REST APIs, Node.js APIs, other NPM packages, or custom logic to provide higher level functions than are served by any single API.

Adjacent to the existing file named zowe-cli-sample-plugin/src/api/Files.ts, create a file Typicode.ts.

Typicode.tsshould contain the following:

import { ITodo } from "./doc/ITodo";
import { RestClient, AbstractSession, ImperativeExpect, Logger } from "@zowe/imperative";

export class Typicode {

    public static readonly TODO_URI = "/todos";

    public static getTodos(session: AbstractSession): Promise<ITodo[]> {
        Logger.getAppLogger().trace("Typicode.getTodos() called");
        return RestClient.getExpectJSON<ITodo[]>(session, Typicode.TODO_URI);

    public static getTodo(session: AbstractSession, id: number): Promise<ITodo> {
        Logger.getAppLogger().trace("Typicode.getTodos() called with id " + id);
        ImperativeExpect.toNotBeNullOrUndefined(id, "id must be provided");
        const resource = Typicode.TODO_URI + "/" + id;
        return RestClient.getExpectJSON<ITodo>(session, resource);

The Typicode class provides two programmatic APIs, getTodos and getTodo, to get an array of ITodo objects or a specific ITodo respectively. The Node.js APIs use @zowe/imperative infrastructure to provide logging, parameter validation, and to call a REST API. See the Imperative CLI Framework documentation (opens new window) for more information.

# Exporting interface and programmatic API for other Node.js applications

Update zowe-cli-sample-plugin/src/index.ts (opens new window) to contain the following:

export * from "./api/doc/ITodo";
export * from "./api/Typicode";

A sample invocation of your API might look similar to the following, if it were used by a separate, standalone Node.js application:

import { Typicode } from "@zowe/zowe-cli-sample-plugin";
import { Session, Imperative } from "@zowe/imperative";
import { inspect } from "util";

const session = new Session({ hostname: "jsonplaceholder.typicode.com"});
(async () => {
    const firstTodo = await Typicode.getTodo(session, 1);
    Imperative.console.debug("First todo was: " + inspect(firstTodo));

# Checkpoint

Issue npm run build to verify a clean compilation and confirm that no lint errors are present. At this point in this tutorial, you have a programmatic API that will be used by your handler or another Node.js application. Next you'll define the command syntax for the command that will use your programmatic Node.js APIs.

# Defining command syntax

Within Zowe CLI, the full command that we want to create is zowe zowe-cli-sample list typicode-todos. Navigate to zowe-cli-sample-plugin/src/cli/list and create a folder typicode-todos. Within this folder, create TypicodeTodos.definition.ts. Its content should be as follows:

import { ICommandDefinition } from "@zowe/imperative";
export const TypicodeTodosDefinition: ICommandDefinition = {
    name: "typicode-todos",
    aliases: ["td"],
    summary: "Lists typicode todos",
    description: "List typicode REST sample data",
    type: "command",
    handler: __dirname + "/TypicodeTodos.handler",
    options: [
            name: "id",
            description: "The todo to list",
            type: "number"

This describes the syntax of your command.

# Defining command handler

Also within the typicode-todos folder, create TypicodeTodos.handler.ts. Add the following code to the new file:

import { ICommandHandler, IHandlerParameters, TextUtils, Session } from "@zowe/imperative";
import { Typicode } from "../../../api/Typicode";
export default class TypicodeTodosHandler implements ICommandHandler {

    public static readonly TYPICODE_HOST = "jsonplaceholder.typicode.com";
    public async process(params: IHandlerParameters): Promise<void> {

        const session = new Session({ hostname: TypicodeTodosHandler.TYPICODE_HOST});
        if (params.arguments.id) {
            const todo = await Typicode.getTodo(session, params.arguments.id);
        } else {
            const todos = await Typicode.getTodos(session);

The if statement checks if a user provides an --id flag. If yes, we call getTodo. Otherwise, we call getTodos. If the Typicode API throws an error, the @zowe/imperative infrastructure will automatically surface this.

# Defining command to list group

Within the file zowe-cli-sample-plugin/src/cli/list/List.definition.ts, add the following code below other import statements near the top of the file:

import { TypicodeTodosDefinition } from "./typicode-todos/TypicodeTodos.definition";

Then add TypicodeTodosDefinition to the children array. For example:

children: [DirectoryContentsDefinition, TypicodeTodosDefinition]

# Checkpoint

Issue npm run build to verify a clean compilation and confirm that no lint errors are present. You now have a handler, definition, and your command has been defined to the list group of the command.

# Using the installed plug-in

Issue the command: zowe zowe-cli-sample list typicode-todos

Refer to zowe zowe-cli-sample list typicode-todos --help for more information about your command and to see how text in the command definition is presented to the end user. You can also see how to use your optional --id flag:


# Summary

You extended an existing Zowe CLI plug-in by introducing a Node.js programmatic API, and you created a command definition with a handler. For an official plugin, you would also add JSDoc (opens new window) to your code and create automated tests.

# Next steps

Try the Developing a new plug-in tutorial next to create a new plug-in for Zowe CLI.