ESOCKETTIMEDOUT when following directions under Anaconda3

[aseedb]

Same problem as described in closed issue #1475 . While trying to install jupyterlab extensions, first an info saying there appears to be problems with network connection. Then an error shows up:
An unexpected error occurred: "https://registry.yarnpkg.com/mdi-react/-/mdi-react-5.1.0.tgz: ESOCKETTIMEDOUT".

This is on a Mac. Uninstalling nodejs with conda and installing it with Homebrew did not help.

This is the output I get:
`
$ jupyter labextension install @jupyter-widgets/[email protected]
Node v11.12.0

/usr/local/bin/npm pack @jupyter-widgets/[email protected]
npm notice
npm notice 📦 @jupyter-widgets/[email protected]
npm notice === Tarball Contents ===
npm notice 2.0kB package.json
npm notice 1.5kB LICENSE
npm notice 2.0kB README.md
npm notice 131B lib/index.d.ts
npm notice 410B lib/index.js
npm notice 2.5kB lib/manager.d.ts
npm notice 6.2kB lib/manager.js
npm notice 1.9kB lib/output.d.ts
npm notice 6.0kB lib/output.js
npm notice 1.1kB lib/plugin.d.ts
npm notice 3.6kB lib/plugin.js
npm notice 829B lib/renderer.d.ts
npm notice 3.0kB lib/renderer.js
npm notice 216B lib/semvercache.d.ts
npm notice 972B lib/semvercache.js
npm notice === Tarball Details ===
npm notice name: @jupyter-widgets/jupyterlab-manager
npm notice version: 0.38.1
npm notice filename: jupyter-widgets-jupyterlab-manager-0.38.1.tgz
npm notice package size: 8.5 kB
npm notice unpacked size: 32.3 kB
npm notice shasum: 1b1e17c929065bd2a93057b2378562c10c3db6c0
npm notice integrity: sha512-JutIwjs2jq6qW[...]Phr69YQ+qQZ/Q==
npm notice total files: 15
npm notice
jupyter-widgets-jupyterlab-manager-0.38.1.tgz
Node v11.12.0

node /Users/bzuber/anaconda3/lib/python3.6/site-packages/jupyterlab/staging/yarn.js install
yarn install v1.9.4
info No lockfile found.
[1/5] 🔍 Validating package.json...
[2/5] 🔍 Resolving packages...
warning @jupyterlab/application > @jupyterlab/apputils > react > fbjs > [email protected]: core-js@<2.6.5 is no longer maintained. Please, upgrade to core-js@3 or at least to actual version of core-js@2.
warning jupyterlab-chart-editor > react-chart-editor > plotly.js > mapbox-gl > @mapbox/[email protected]: This
warning jupyterlab-chart-editor > react-chart-editor > plotly.js > ndarray-fill > cwise > static-module > through2 > xtend > [email protected]:
warning css-loader > cssnano > autoprefixer > [email protected]: Browserslist 2 could fail on reading Browserslist >3.0 config used in other tools.
warning css-loader > cssnano > postcss-merge-rules > [email protected]: Browserslist 2 could fail on reading Browserslist >3.0 config used in other tools.
warning css-loader > cssnano > postcss-merge-rules > caniuse-api > [email protected]: Browserslist 2 could fail on reading Browserslist >3.0 config used in other tools.
[3/5] 🚚 Fetching packages...
[----------------------------------------------------------------------------------------------------------------] 0/1336(node:31071) [DEP0005] DeprecationWarning: Buffer() is deprecated due to security and usability issues. Please use the Buffer.alloc(), Buffer.allocUnsafe(), or Buffer.from() methods instead.
info There appears to be trouble with your network connection. Retrying...
info There appears to be trouble with your network connection. Retrying...
info There appears to be trouble with your network connection. Retrying...
info There appears to be trouble with your network connection. Retrying...
info There appears to be trouble with your network connection. Retrying...
error An unexpected error occurred: "https://registry.yarnpkg.com/mdi-react/-/mdi-react-5.1.0.tgz: ESOCKETTIMEDOUT".
info If you think this is a bug, please open a bug report with the information provided in "/Users/bzuber/anaconda3/share/jupyter/lab/staging/yarn-error.log".
info Visit https://yarnpkg.com/en/docs/cli/install for documentation about this command.
info There appears to be trouble with your network connection. Retrying...
info There appears to be trouble with your network connection. Retrying...
info There appears to be trouble with your network connection. Retrying...
node /Users/bzuber/anaconda3/lib/python3.6/site-packages/jupyterlab/staging/yarn.js run build
yarn run v1.9.4
$ webpack
/bin/sh: webpack: command not found
error Command failed with exit code 127.
info Visit https://yarnpkg.com/en/docs/cli/run for documentation about this command.`

[aseedb]

Found the solution:

see jupyterlab/jupyterlab#5943 (comment)
and for longer explanation :
yarnpkg/yarn#5540 (comment)