Dockerfile: npm errors when building an image

I am on Ubuntu 18.04.4 and using the current master branch (decker@bbf296e2). When trying to build a docker image via docker build -t decker . (in the root directory) it fails with an error message:

(cd jquery && npm run build)
/bin/bash: npm: command not found
make[1]: *** [jquery/dist/jquery.min.js] Error 127
symlinks.mk:55: recipe for target 'jquery/dist/jquery.min.js' failed
make[1]: Leaving directory '/decker/third-party'
makefile:15: recipe for target 'clean-build' failed
make: *** [clean-build] Error 2
The command '/bin/sh -c make ${MAKE_FLAGS} install' returned a non-zero code: 2

So, I just added RUN apt-get install -y npm to the Dockerfile; however, the building process runs into another error:

> jquery@4.0.0-pre build /decker/third-party/jquery
> npm install && grunt

npm WARN deprecated resolve-url@0.2.1: https://github.com/lydell/resolve-url#deprecated
npm WARN deprecated urix@0.1.0: Please see https://github.com/lydell/urix#deprecated
npm WARN deprecated nomnom@1.8.1: Package no longer supported. Contact support@npmjs.com for more info.
npm WARN deprecated request@2.88.2: request has been deprecated, see https://github.com/request/request/issues/3142
npm WARN deprecated chokidar@2.1.8: Chokidar 2 will break on node v14+. Upgrade to chokidar 3 with 15x less dependencies.
npm WARN deprecated core-js@2.6.11: core-js@<3 is no longer maintained and not recommended for usage due to the number of issues. Please, upgrade your dependencies to the actual version of core-js@3.
npm WARN deprecated to-iso-string@0.0.2: to-iso-string has been deprecated, use @segment/to-iso-string instead.
npm WARN deprecated mkdirp@0.5.1: Legacy versions of mkdirp are no longer supported. Please update to mkdirp 1.x. (Note that the API surface has changed to use Promises in 1.x.)
npm WARN deprecated jade@0.26.3: Jade has been renamed to pug, please install the latest version of pug instead of jade
npm WARN deprecated minimatch@0.3.0: Please update to minimatch 3.0.2 or higher to avoid a RegExp DoS issue
npm WARN deprecated mkdirp@0.3.0: Legacy versions of mkdirp are no longer supported. Please update to mkdirp 1.x. (Note that the API surface has changed to use Promises in 1.x.)
npm WARN deprecated samsam@1.1.2: This package has been deprecated in favour of @sinonjs/samsam
npm WARN deprecated formatio@1.1.1: This package is unmaintained. Use @sinonjs/formatio instead
npm ERR! Linux 5.3.0-53-generic
npm ERR! argv "/usr/bin/node" "/usr/bin/npm" "install"
npm ERR! node v8.10.0
npm ERR! npm  v3.5.2
npm ERR! code EMISSINGARG

npm ERR! typeerror Error: Missing required argument #1
npm ERR! typeerror     at andLogAndFinish (/usr/share/npm/lib/fetch-package-metadata.js:31:3)
npm ERR! typeerror     at fetchPackageMetadata (/usr/share/npm/lib/fetch-package-metadata.js:51:22)
npm ERR! typeerror     at resolveWithNewModule (/usr/share/npm/lib/install/deps.js:456:12)
npm ERR! typeerror     at /usr/share/npm/lib/install/deps.js:457:7
npm ERR! typeerror     at /usr/share/npm/node_modules/iferr/index.js:13:50
npm ERR! typeerror     at /usr/share/npm/lib/fetch-package-metadata.js:37:12
npm ERR! typeerror     at addRequestedAndFinish (/usr/share/npm/lib/fetch-package-metadata.js:82:5)
npm ERR! typeerror     at returnAndAddMetadata (/usr/share/npm/lib/fetch-package-metadata.js:117:7)
npm ERR! typeerror     at pickVersionFromRegistryDocument (/usr/share/npm/lib/fetch-package-metadata.js:134:20)
npm ERR! typeerror     at /usr/share/npm/node_modules/iferr/index.js:13:50
npm ERR! typeerror This is an error with npm itself. Please report this error at:
npm ERR! typeerror     <http://github.com/npm/npm/issues>


npm ERR! Please include the following file with any support request:
npm ERR!     /decker/third-party/jquery/npm-debug.log

npm ERR! Linux 5.3.0-53-generic
npm ERR! argv "/usr/bin/node" "/usr/bin/npm" "run" "build"
npm ERR! node v8.10.0
npm ERR! npm  v3.5.2
npm ERR! code ELIFECYCLE
npm ERR! jquery@4.0.0-pre build: `npm install && grunt`
npm ERR! Exit status 1
npm ERR! 
npm ERR! Failed at the jquery@4.0.0-pre build script 'npm install && grunt'.
npm ERR! Make sure you have the latest version of node.js and npm installed.
npm ERR! If you do, this is most likely a problem with the jquery package,
npm ERR! not with npm itself.
npm ERR! Tell the author that this fails on your system:
npm ERR!     npm install && grunt
npm ERR! You can get information on how to open an issue for this project with:
npm ERR!     npm bugs jquery
npm ERR! Or if that isn't available, you can get their info via:
npm ERR!     npm owner ls jquery
npm ERR! There is likely additional logging output above.

npm ERR! Please include the following file with any support request:
npm ERR!     /decker/third-party/jquery/npm-debug.log
symlinks.mk:55: recipe for target 'jquery/dist/jquery.min.js' failed
make[1]: Leaving directory '/decker/third-party'
make[1]: *** [jquery/dist/jquery.min.js] Error 1
makefile:15: recipe for target 'clean-build' failed
make: *** [clean-build] Error 2