developmentDependencies

DevelopmentDependencies, or devDependencies, is a field in a package.json file used by Node.js package managers to designate packages that are only required during development, testing, or build time. These can include test frameworks, linters, transpilers, bundlers, and other tooling. They are separate from dependencies, which are needed at runtime by consuming applications.

In a typical project, devDependencies list tools such as jest or mocha for testing, eslint for linting, typescript or babel for compilation, and webpack or rollup for bundling. These items facilitate development and quality assurance but are not required for the package to run in a production environment. When a package is published, its devDependencies are not installed for consumers that install the package as a dependency, helping keep production installations lean.

Installing dependencies for development usually includes both dependencies and devDependencies, via commands like npm install. To install only production dependencies, commands such as npm install --production or npm ci --omit=dev (depending on the version) are commonly used. This behavior can be influenced by environment variables like NODE_ENV.

DevDependencies are recorded in lockfiles (e.g., package-lock.json) to ensure reproducible installs. In monorepos or workspaces, devDependencies can be scoped to individual packages. While the concept is most associated with npm, it is a standard part of other JavaScript package managers as well, with variations in commands and configuration.