npm install

TL;DR

npm version 6.4.1.
Use NODE_ENV=production npm ci for production build. E.g. in Dockerfile.
Use NODE_ENV=production npm install --no-audit with --offline or --prefer-offline when you are trying different package’s. E.g. finding which dependency works or breaks.
Use npm ci whenever you think of npm install.
Use npm install in any other cases.

$ rm -fr ./node_modules && time npm install
real	1m37.645s
user	1m21.663s
sys	0m32.953s

The slowest.

$ rm -fr ./node_modules && time npm install --prefer-offline
real	1m10.059s
user	1m8.615s
sys	0m33.535s

--prefere-offline is faster than without it.

$ rm -fr ./node_modules && time npm install --offline
real	0m59.658s
user	1m2.794s
sys	0m30.149s

--offline is faster than --prefer-offline.

$ rm -fr ./node_modules && time npm install --offline --no-audit
real	0m54.984s
user	1m0.524s
sys	0m29.629s

--no-audit makes it a little bit faster.

$ rm -fr ./node_modules && time npm install --offline --no-audit --only=prod
real	0m35.677s
user	0m39.828s
sys	0m16.780s

--only=prod makes it much faster.

$ rm -fr ./node_modules && export NODE_ENV=production && time npm install --offline --no-audit
real	0m32.578s
user	0m38.242s
sys	0m16.573s

NODE_ENV=production is faster than --only-prod.

$ export NODE_ENV=production && time npm ci --offline --no-audit
real	0m22.572s
user	0m20.928s
sys	0m16.034s

npm ci is faster than npm install.

$ export NODE_ENV=production && time npm ci --no-audit
real	0m25.646s
user	0m17.084s
sys	0m13.334s

--offline makes npm ci a little bit slower.

$ export NODE_ENV=production && time npm ci
real	0m17.636s
user	0m16.791s
sys	0m9.699s

--no-audit also makes npm ci a little slower.

$ time npm ci
real	0m35.362s
user	0m18.570s
sys	0m16.471s

NODE_ENV=production makes npm ci much faster.