# Error Using the Official vtk.js Tutorials (slides/video)
**URL:** https://discourse.vtk.org/t/error-using-the-official-vtk-js-tutorials-slides-video/6003
**Category:** Support
**Created:** [June 15, 2021, 7:56pm UTC](https://discourse.vtk.org/t/error-using-the-official-vtk-js-tutorials-slides-video/6003 "2021-06-15T19:56:38Z")
**Posts on this page:** 2
**Page:** 1
### Author:  [@davidshq](https://discourse.vtk.org/u/davidshq)
#### Post date: [June 15, 2021, 7:56pm UTC](https://discourse.vtk.org/t/error-using-the-official-vtk-js-tutorials-slides-video/6003/1 "2021-06-15T19:56:38Z")
I’ve run into some challenges following the [(official) video tutorial series on using VTK.js](https://kitware.github.io/vtk-js/docs/tutorial.html).
I’m on [part 2](https://vimeo.com/375521036) and have built a project with the code provided. When I attempt to run `npm run dev` I receive an error about a missing `webpack-cli/bin/config-yargs`.
I discovered a former thread in which this issue was discussed and resolved:
> [@Problem when trying to setup first VTKJS project](https://discourse.vtk.org/t/problem-when-trying-to-setup-first-vtkjs-project/4761):
>
> Hello all, my goal is to have a web app with a bootstrap-powered interface and an embedded VTKJS-based render view to visualize 3D volumes. I’m trying to use node to build/start my first VTKJS project according to the following page: However, when trying to run the server ($npm start), the following error message appears: $ npm start vtk-js-4@1.0.0 start C:\work\research\web-studies\vtk-js-4 webpack-dev-server --content-base ./dist internal/modules/cjs/loader.js:883 throw err; ^ Er…
(You can look at the above thread to see the full error regarding `config-yargs`)
I followed the instructions (modifying the `package.json` to no longer refer to `webpack-dev-server` and instead used `webpack serve` as shown below:
```json
"dev": "webpack-dev-server --mode=development",
// changed to:
"dev": "webpack serve --mode=development --content-base=./dist",
```
Now I receive a different error when running `npm run dev`:
```terminal
> vtkex@1.0.0 dev /vtkex
> webpack serve --content-base ./dist
(node:54204) UnhandledPromiseRejectionWarning: TypeError: Class constructor ServeCommand cannot be invoked without 'new'
at run (/vtkex/node_modules/webpack-cli/lib/utils/resolve-command.js:33:12)
at Command. (/vtkex/node_modules/webpack-cli/lib/utils/arg-parser.js:34:58)
at Command.listener [as _actionHandler] (/vtkex/node_modules/commander/index.js:426:31)
at Command._parseCommand (vtkex/node_modules/commander/index.js:1002:14)
at Command._dispatchSubcommand (/vtkex/node_modules/commander/index.js:953:18)
at Command._parseCommand (/vtkex/node_modules/commander/index.js:970:12)
at Command.parse (/vtkex/node_modules/commander/index.js:801:10)
at argParser (/vtkex/node_modules/webpack-cli/lib/utils/arg-parser.js:164:27)
at runCLI (/vtkex/node_modules/webpack-cli/lib/bootstrap.js:11:24)
at Object. (/vtkex/node_modules/webpack-cli/bin/cli.js:24:5)
(Use `node --trace-warnings ...` to show where the warning was created)
(node:54204) UnhandledPromiseRejectionWarning: Unhandled promise rejection.
This error originated either by throwing inside of an async function without a
catch block, or by rejecting a promise which was not handled with .catch(). To
terminate the node process on unhandled promise rejection, use the CLI
flag `--unhandled-rejections=strict`
(see https://nodejs.org/api/cli.html#cli_unhandled_rejections_mode).
(rejection id: 2)
(node:54204) [DEP0018] DeprecationWarning: Unhandled promise rejections are
deprecated. In the future, promise rejections that are not handled will terminate
the Node.js process with a non-zero exit code.
```
I tried changing the `package.json` file again:
```json
"dev": "webpack --mode=development"
```
This builds the app successfully _but doesn’t execute it_.
I altered `package.json` again:
```json
"dev": "webpack serve --content-base ./dist"
```
And running `npm run dev` still causes the same error message.
I then tried installing `webpack-server` as @Rafael_March did:
```terminal
$ npm i webpack-serve
$ npm run dev
```
I tried the same `package.json` edits I’ve referenced above but they all return the same error (excluding `webpack --mode=development` which, as noted above, compiles but doesn’t run the app).
I’m hoping someone can help me resolve this issue and will update this thread as I discover more.
I also thought folks might want to know so the official tutorials/docs could be updated since this tutorial series appears to be the primary method of learning vtk.js.
When a resolution is found, I’d like to see the Vimeo video (and separate PowerPoint slides) have text notes overlaid that explain the needed changes to avoid the same issues for others (I know rerecording the entire video may not be feasible).
I also noticed that the example `package.json` for this project includes calls to `web-dev-server`:
>
It may be worthwhile updating these files as well. Once we find the resolution I’m happy to submit a patch to do so, if that is helpful.
I also noticed that the approach used in these tutorials/videos is the older approach of installing `vtk.js` instead of `@kitware/vtk.js`. I attempted to migrate my instance from using the older to the newer (as recommended [here](https://kitware.github.io/vtk-js/docs/intro_vtk_as_es6_dependency.html) but ran into some issues and have abandoned the migration for the moment.
---
### Author:  [@Forrest](https://discourse.vtk.org/u/Forrest)
#### Post date: [June 18, 2021, 8:25pm UTC](https://discourse.vtk.org/t/error-using-the-official-vtk-js-tutorials-slides-video/6003/2 "2021-06-18T20:25:29Z")
Hi, thanks for the detailed information. I will take note and work to update both the slides, video, and examples.
What sort of errors were you getting when you were migrating to `@kitware/vtk.js`?