Installed module 'express-validator' cannot be found in NodeJS/Express project

Question

I want to validate the input that the endpoint receives upon invoking it. Therefore, I installed express-validator in my NodeJS web application. However, when I try to make use of it, it throws the error:

Cannot find module 'express-validator' or its corresponding type declarations

This happens, when I import it (i.e., import { validationResult } from "express-validator";) or set it as an constant and require it. In the latter, it states that it cannot find the module. I have dockerized the project and this is the the dockerfile I have set up:

FROM node:12

WORKDIR /app

COPY package*.json ./

RUN npm install

COPY . .

EXPOSE 8000

CMD ["npm", "run", "dev"]

Currently, I am not running a production version, which is why I am running with dev. This is my docker-compose file:

services:
  db:
    image: postgres:12
    environment:
      - POSTGRES_DB=server_side
      - POSTGRES_USER=postgres
      - POSTGRES_PASSWORD=123321
  app:
    build:
      context: .
      dockerfile: Dockerfile
    volumes:
      - ./src:/app/src
    ports:
      - "8000:8000"
    depends_on:
      - db
    environment:
      - POSTGRES_DB=server_side
      - POSTGRES_USER=postgres
      - POSTGRES_PASSWORD=123321
      - POSTGRES_HOST=db

When installing the module, it gets added to my dependencies:

{
  "name": "Servier-side",
  "version": "1.0.0",
  "description": "",
  "main": "index.js",
  "scripts": {
    "build": "tsc",
    "dev": "concurrently \"nodemon\" \"nodemon -x tsoa spec\"",
    "start": "node build/index.js",
    "predev": "npm run swagger",
    "prebuild": "npm run swagger",
    "swagger": "tsoa spec",
    "typeorm": "node --require ts-node/register ./node_modules/typeorm/cli.js",
    "migrate:generate": "npm run typeorm migration:generate -- -n",
    "migrate:run": "npm run typeorm migration:run",
    "migrate:revert": "npm run typeorm migration:revert",
    "schema:drop": "npm run typeorm schema:drop"
  },
  "keywords": [],
  "author": "",
  "license": "ISC",
  "devDependencies": {
    "@types/express": "^4.17.13",
    "@types/morgan": "^1.9.3",
    "@types/node": "^16.11.10",
    "@types/swagger-ui-express": "^4.1.3",
    "concurrently": "^6.4.0",
    "nodemon": "^2.0.15",
    "ts-node": "^10.4.0",
    "typescript": "^4.5.2"
  },
  "dependencies": {
    "express": "^4.17.1",
    "express-validator": "^6.13.0",
    "morgan": "^1.10.0",
    "pg": "^8.7.1",
    "reflect-metadata": "^0.1.13",
    "swagger-ui-express": "^4.1.6",
    "tsoa": "^3.2.1",
    "typeorm": "^0.2.41"
  },
  "nodemonConfig": {
    "watch": [
      "src"
    ],
    "ext": "ts",
    "exec": "ts-node src/index.ts"
  }
}

I would really appreciate if someone could shed light on the matter. Just for the sake of excluding possible reasons, I also tried with Joi, but I ended up with the same issue. So, what I would like to understand is what is causing the issue - Why does is work for the rest of the dependencies and not this one and what should be done to resolve the issue?

Answer 1

Running docker compose with the build flag docker-compose up --build fixed the issue.