dockerfile

# Use the official Node.js image as the base image, specifically the "slim" variant, 
#which is a smaller version of the image.
FROM node:slim

# Set the environment variable NODE_ENV to "development". 
#This can be used by your application to determine the environment it's running in.
ENV NODE_ENV development

# Set the working directory in the container to /express-docker.
# All subsequent commands will be run in this directory.
WORKDIR /express-docker

# Copy all files from the current directory on the host machine to the working directory in the container.
COPY . .

# Run the command "npm install" to install all dependencies listed in the package.json file.
RUN npm install

# Inform Docker that the container will listen on port 3000 at runtime.
EXPOSE 3000

# Specify the command to run when the container starts.
# Here, it will run "node index.js" to start your Node.js application.
CMD [ "node", "index.js" ]