# Source code

The Apify Actor's source code placement is defined by its [Dockerfile](https://pr-2338.preview.docs.apify.com/platform/actors/development/actor-definition/dockerfile.md). If you have created the Actor from one of Apify's [templates](https://apify.com/templates) then it's by convention placed in the `/src` directory.

You have the flexibility to choose any programming language, technologies, and dependencies (such as Chrome browser, Selenium, Cypress, or others) for your projects. The only requirement is to define a Dockerfile that builds the image for your Actor, including all dependencies and your source code.

## Example setup

Let's take a look at the example JavaScript Actor's source code. The following Dockerfile:


```
FROM apify/actor-node:20

COPY package*.json ./

RUN npm --quiet set progress=false \
    && npm install --omit=dev --omit=optional \
    && echo "Installed NPM packages:" \
    && (npm list --omit=dev --all || true) \
    && echo "Node.js version:" \
    && node --version \
    && echo "NPM version:" \
    && npm --version \
    && rm -r ~/.npm

COPY . ./

CMD npm start --silent
```


This `Dockerfile` does the following tasks:

1. Builds the Actor from the `apify/actor-node:20` base image.


   ```
   FROM apify/actor-node:20
   ```


2. Copies the `package.json` and `package-lock.json` files to the image.


   ```
   COPY package*.json ./
   ```


3. Installs the npm packages specified in package.json, omitting development and optional dependencies.


   ```
   RUN npm --quiet set progress=false \
       && npm install --omit=dev --omit=optional \
       && echo "Installed NPM packages:" \
       && (npm list --omit=dev --all || true) \
       && echo "Node.js version:" \
       && node --version \
       && echo "NPM version:" \
       && npm --version \
       && rm -r ~/.npm
   ```


4. Copies the rest of the source code to the image


   ```
   COPY . ./
   ```


5. Runs the `npm start` command defined in `package.json`


   ```
   CMD npm start --silent
   ```


Optimized build cache

By copying the `package.json` and `package-lock.json` files and installing dependencies before the rest of the source code, you can take advantage of Docker's caching mechanism. This approach ensures that dependencies are only reinstalled when the `package.json` or `package-lock.json` files change, significantly reducing build times. Since the installation of dependencies is often the most time-consuming part of the build process, this optimization can lead to substantial performance improvements, especially for larger projects with many dependencies.

### `package.json`

The `package.json` file defines the `npm start` command:


```
{
    "name": "getting-started-node",
    "version": "0.0.1",
    "type": "module",
    "description": "This is an example of an Apify Actor.",
    "dependencies": {
        "apify": "^3.0.0"
    },
    "devDependencies": {},
    "scripts": {
        "start": "node src/main.js",
        "test": "echo \"Error: oops, the Actor has no tests yet, sad!\" && exit 1"
    },
    "author": "It's not you; it's me",
    "license": "ISC"
}
```


When the Actor starts, the `src/main.js` file is executed.