post an online link for viz.js and the introduced code.

1. Compare whether the local js file is consistent with the CDN file
2. You can add ts-loader
3 to the webpack configuration. See if viz.js has npm packages

indicates that its online version has been compiled into js.
npm downloads the ts source code. In general, publishing to npm should provide a packaged umd specification code. You can check the main attribute in the package.json in that package to see which file it points to. If it does point to the ts source code, then you have to add a plug-in for ts processing in the build/webpack.base.conf.js of your project, that is, the specific configuration of ts-loader, needs to check the documentation.

of course, the easiest thing is for you to download the online version of the code directly and use it as source code in your project

the question is bypassed. The current solution for
is to place the local viz.js in the static directory , and then introduce in index.html with the script tag.
although the viz.js file still displays syntax errors in VS Code, it does not affect packaging and running at this time.