What is the difference between npm install and npm ci

npm install and npm ci are two commonly used commands in the Node.js ecosystem for installing dependencies, but they operate differently in terms of their purpose and behavior.

1. npm install:

   • Purpose: npm install is one of the most commonly used commands for installing dependencies. It installs modules based on the dependencies listed in the package.json file and can update the package-lock.json file.
   • Behavior: npm install searches for and installs the latest versions of dependencies based on the version ranges defined in package.json or npm-shrinkwrap.json. If package-lock.json exists, it also considers this file, but it allows updating dependencies according to the semantic versioning constraints specified in package.json.
   • Example: If your package.json specifies a package version as ^1.0.0, this means that running npm install can install any 1.x.x version of the package as long as it is the latest and satisfies the constraints in package.json.

2. npm ci:

   • Purpose: npm ci (where 'ci' stands for Continuous Integration) is primarily used in automated environments such as test platforms, continuous integration, and deployment pipelines. This command must be run when package-lock.json or npm-shrinkwrap.json files are present.
   • Behavior: npm ci ignores the dependencies listed in package.json and strictly installs dependencies based on the specific versions defined in package-lock.json or npm-shrinkwrap.json. This ensures consistency across different environments and among developers.
   • Speed: npm ci is typically faster than npm install because it skips certain user-facing features, such as updating the package-lock.json file or installing new versions of packages.
   • Example: If you deploy your project codebase along with the package-lock.json file to a continuous integration server, running npm ci will ensure that the dependencies installed on the server match exactly those used in your local development environment.

In summary, if you want to install or update dependencies in your local development environment, you typically use npm install. If you're in an automated environment and need a reproducible, deterministic dependency installation process, you would use npm ci.