What does "publicPath" in Webpack do?

Webpack docs state that output.publicPath is:

The output.path from the view of the JavaScript.

Could you please elaborate on what this actually means?

I use output.path and output.filename to specify where Webpack should output the result, but I’m not sure what to put in output.publicPath and whether it is required.

module.exports = {
  output: {
    path: path.resolve("./examples/dist"),
    filename: "app.js",
    publicPath: "What should I put here?"   
  } 
}

output.path

Local disk directory to store all your output files (Absolute path).

Example: path.join(__dirname, "build/")

Webpack will output everything into localdisk/path-to-your-project/build/

output.publicPath

Where you uploaded your bundled files. (absolute path, or relative to main HTML file)

Example: /assets/

Assumed you deployed the app at server root http://server/.

By using /assets/, the app will find webpack assets at: http://server/assets/. Under the hood, every urls that webpack encounters will be re-written to begin with "/assets/".

src="picture.jpg" Re-writes ➡ src="/assets/picture.jpg"

Accessed by: (http://server/assets/picture.jpg)

---

src="/img/picture.jpg" Re-writes ➡ src="/assets/img/picture.jpg"

Accessed by: (http://server/assets/img/picture.jpg)

When executed in the browser, webpack needs to know where you'll host the generated bundle. Thus it is able to request additional chunks (when using code splitting) or referenced files loaded via the file-loader or url-loader respectively.

For example: If you configure your http server to host the generated bundle under /assets/ you should write: publicPath: "/assets/"

the publicPath is just used for dev purpose, I was confused at first time I saw this config property, but it makes sense now that I've used webpack for a while

suppose you put all your js source file under src folder, and you config your webpack to build the source file to dist folder with output.path.

But you want to serve your static assets under a more meaningful location like webroot/public/assets, this time you can use out.publicPath='/webroot/public/assets', so that in your html, you can reference your js with <script src="/webroot/public/assets/bundle.js"></script>.

when you request webroot/public/assets/bundle.js the webpack-dev-server will find the js under the dist folder

Update:

thanks for Charlie Martin to correct my answer

original: the publicPath is just used for dev purpose, this is not just for dev purpose

No, this option is useful in the dev server, but its intention is for asynchronously loading script bundles in production. Say you have a very large single page application (for example Facebook). Facebook wouldn't want to serve all of its javascript every time you load the homepage, so it serves only whats needed on the homepage. Then, when you go to your profile, it loads some more javascript for that page with ajax. This option tells it where on your server to load that bundle from