Dependency

You might say

I just downloaded the project and it reports a missing module. Is the code broken?

Code packages written by others that a project needs; they must be installed before the project runsCloning a repo downloads only the package.json manifest, not the packages themselves; running directly throws 'Cannot find module'. Running an install command fetches third-party code packages into your local folder before the project can boot; swapping machines or pulling new code requires repeating this step.

Know first

npm

Dependency

From clone to start: when dependencies enter the project

my-first-page/No node_modules yet

package.jsonRecords which packages are needed

src/

node_modules/Does not exist

Terminal

$ npm start
Error: Cannot find module 'react'
Dependencies are not installed yet

The list is there but not the packages: install before starting

For a missing module, separate three causes: never installed, version mismatch, or a wrong import path—each reports differently.

Why dependencies need a separate install step

The project stores a list, not the packages: The repository usually holds one file that records which packages and versions the project needs; the packages themselves are downloaded on demand and are not versioned.

Installing is a one-time preparation: The install command reads the list and downloads packages into the project folder. On another machine or after re-cloning, installation must be repeated.

Errors map to different causes: Cannot find module first suggests dependencies were never installed. If it persists after installing, check the version match and whether the import path is wrong.

Quick checkChoose the best answer

A newly cloned project reports Cannot find module 'react' when running npm start. What should happen next?

Ask AI to rewrite the code without importing reactReinstall Node.js because a missing module is an environment problemRun npm install first, then start the project again

You can say this to an AI Agent

The freshly cloned project reports Cannot find module. Run the dependency install command first, confirm every package in the manifest is installed, then start again. If installation fails, explain which package failed and why instead of working around it in business code.

Learn next

1npm→2Semantic Versioning→

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