Node.js errorNode.js: “Error: Cannot find module”

Why Node.js can’t find it, and the fix

1. 01

   The package is not installed where the code runs

   “If it is not found there, then it moves to the parent directory, and so on, until the root of the file system is reached.” Node.js, Modules: CommonJS modules

   For a bare name like 'express', Node.js walks up from the current file through every node_modules folder to the root of the disk. If the package is not in any of them, the error appears. This is common after cloning a repo, after switching branches that changed package.json, or on a server where the install ran in a different folder.

   # in the folder that holds package.json
   npm install
   
   # a single missing package
   npm install express

2. 02

   Production skipped devDependencies

   Hosts and Docker images often install with npm ci --omit=dev or NODE_ENV=production. Anything the running app needs at runtime must be in dependencies. A package used only by the build (TypeScript, a bundler) can stay in devDependencies if the build runs before the dev packages are dropped.

   # move a runtime package to dependencies
   npm install --save-prod dotenv

3. 03

   The relative path is wrong

   A name starting with ./ or ../ is resolved from the folder of the file that contains the require, not from where you started node. Check the spelling and the case: macOS ignores case by default, but Linux servers and most CI do not, so ./Utils/db works on a Mac and fails on deploy. With ES modules (import), include the file extension, such as ./db.js.

4. 04

   The entry file is not built yet

   Errors like Cannot find module '/app/dist/index.js' mean the start command points at build output that does not exist. Run the build before start (npm run build, then npm start), check the outDir in tsconfig.json matches the path in package.json, and make sure the build output is not excluded from the deploy.

   // package.json
   "scripts": {
     "build": "tsc",
     "start": "node dist/index.js"
   }

Checked against the vendor’s docs on November 7, 2026: Node.js: Modules: CommonJS modules (loading from node_modules folders); Node.js: Errors (MODULE_NOT_FOUND).

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Related: “Cannot use import statement outside a module” · Vercel “Module not found: Can’t resolve” · Node.js ENOENT: no such file or directory · Node.js ERR_MODULE_NOT_FOUND