Error: spawn npm ENOENT when running instructions for creating Auth0 extension on Windows

[hsluoyz]

I want to develop my own Auth0 extension. In https://manage.auth0.com/#/extensions, I clicked the +CREATE EXTENSION button. It said: Want to write your own extension? Check out this command line tool. I clicked the link. It gave me the Development Instructions as follows:

1. Install wt (requires Node.js)

$ npm install -g wt-cli

2. Setup wt

$ wt init --container "xxx" --url "https://sandbox.it.auth0.com" --token "xxx" -p "xxx-gallery"

3. Install wt-gallery

$ npm install -g wt-gallery-cli

4. Scaffold a basic extension

$ wt-gallery scaffold sample

5. Deploy your gallery extension

$ cd sample && npm run bundle 
$ wt create ./build/bundle.js --name extension --param xxx="xxx" --param xxx="1.0.0"

When I run the step 4, I encountered the error:

C:\aaa>wt-gallery scaffold sample

[1] Simple Application
[2] React Application
[3] Cron Job

Which type of application do you want to create? 1
Do you want to install dependencies? [y/n]: y
events.js:183
      throw er; // Unhandled 'error' event
      ^

Error: spawn npm ENOENT
    at _errnoException (util.js:1022:11)
    at Process.ChildProcess._handle.onexit (internal/child_process.js:190:19)
    at onErrorNT (internal/child_process.js:372:16)
    at _combinedTickCallback (internal/process/next_tick.js:138:11)
    at process._tickCallback (internal/process/next_tick.js:180:9)

C:\aaa>

I'm using a Windows 10 x64 OS, and NodeJS 8.9.4 LTS. The shell is an administrator CMD.

Can anyone tell me how to fix it? Thanks.