Node "Cannot find module 'typescript'" - Fix Missing tsc in CI

TypeScript-driven tools - tsc, ts-node, tsx, type-aware linters - require the typescript package to be resolvable. In CI it goes missing when devDependencies are stripped, a peer is unmet, or it was only ever installed globally.

What this error means

A build or type-check step fails with Cannot find module 'typescript' (often from ts-node or a tool that loads tsc). It works locally where typescript is installed but fails in a CI job that does not install it.

Node output

Error: Cannot find module 'typescript'
Require stack:
- /app/node_modules/ts-node/dist/index.js
    at Function._resolveFilename (node:internal/modules/cjs/loader)
    ... code: 'MODULE_NOT_FOUND'

Common causes

typescript is a devDependency stripped in a prod install

A --omit=dev (or NODE_ENV=production) install drops typescript, so any tool needing it cannot resolve it.

typescript is an unmet peer of a tool

ts-node/tsx/type-aware ESLint declare typescript as a peer. If it is not in the project, the tool cannot load it.

How to fix it

Install typescript as a project dependency

Add typescript to devDependencies and run the build with dev deps present.

Terminal

npm install -D typescript
# build with dev deps (do not strip them before tsc runs)
npm ci
npx tsc --version

Keep build tooling for the build step

Do not run --omit=dev before the TypeScript build.
Ensure typescript satisfies the peer range of ts-node/tsx/eslint.
Prune to production only after the build is done.

How to prevent it

Declare typescript in devDependencies, not globally.
Build before pruning dev deps.
Match the typescript version to tool peer ranges.