npm ci is a new npm command introduced in npm 6. Let's see how this command is different with npm install

NPM CI

npm ci characteristics:

• Faster than npm install 🐇
• If node_modules present, it will be deleted to ensure clean state 💪🏼
• It can't be used to install new dependency or update existing dependency
• It will use package-lock.json to install all dependencies
• It never modifies package.json or package-lock.json file
• It will throw error if version in package.json do not match with package-lock.json
• Suitable for automated environment such as continuous integration

npm ci will always delete node modules

npm ci will throw error if version is different in package.json vs package-lock.json

NPM Install

npm install characteristics:

• To install a new dependency or update existing dependency
• It could modify package-lock.json when you install a new dependency or update existing one
• It could install different version vs the one that you specify in package.json if you use ^ or ~ 😓

For example, the version in package.json is ~4.17.0, but after running npm install, in package-lock.json, it will use 4.17.20 (the latest patch version)

Conclusion

Use npm ci for automated environment such as CI/CD while npm install to install a new dependency or update dependencies.