Add conventional npm scripts

Signed-off-by: Christoph Wurst <christoph@winzerhof-wurst.at>

developer_manual/app/index.rst

@@ -7,6 +7,7 @@ App development
 
    intro
    tutorial
+   npm
    requests/index
    view/index
    storage/index

developer_manual/app/npm.rst

@@ -0,0 +1,101 @@
+===
+NPM
+===
+
+The node package manager ``npm`` is a widely used tool to manage JavaScript dependencies. In
+order to make the project setup easier for everybody, we recommend to follow the convention
+of typical scripts like ``build``, ``watch`` and ``test`` in the ``package.json`` file.
+
+You can find more info about this convention on blog posts like `this https://www.keithcirkel.co.uk/how-to-use-npm-as-a-build-tool/`_.
+
+npm build
+---------
+
+Once ``npm install`` (``npm i`` for short) has been run to install all dependencies specified
+on ``package.json``, one typically has to build the project. Building can happen with tools like
+Webpack, Grunt or similar. To unify the build command across Nextcoud apps, just add the build
+command(s) as ``build`` script to your.
+
+For apps that use webpack, this might look like this:
+
+.. code-block:: json
+
+  {
+    "name": "myapp",
+    "scripts": {
+      "build": "webpack --progress --config webpack.prod.js"
+    },
+    "devDependencies": {
+      "webpack": "^4.26.1",
+      "webpack-cli": "^3.1.2",
+    }
+  }
+
+You can then run ``npm build`` in your app's root directory to invoke the build process.
+
+See the `npm-build docs https://docs.npmjs.com/cli/build`_ for more info.
+
+npm run watch
+-------------
+
+Since building the release version of JavaScript scripts can be slow, apps often have a dedicated
+build step for development that builds faster and enables debug output. Additionally, it instructs
+the bundler to listen to file changes and (incrementally) rebuild the project.
+
+This command should be added to ``package.json`` as ``watch`` script:
+
+.. code-block:: json
+
+  {
+    "name": "myapp",
+    "scripts": {
+      "build": "webpack --progress --config webpack.prod.js",
+      "watch": "webpack --progress --config webpack.dev.js --watch"
+    },
+    "devDependencies": {
+      "webpack": "^4.26.1",
+      "webpack-cli": "^3.1.2",
+    }
+  }
+
+The development build is invoked with ``npm run dev``.
+
+npm test
+--------
+
+Npm will run the ``test`` script when ``npm test`` is run, hence you might want to specify the
+test command(s) like this:
+
+.. code-block:: json
+
+  {
+    "scripts": {
+      "test": "mocha-webpack --webpack-config webpack.test.js --require src/tests/setup.js \"src/tests/**/*.spec.js\""
+    }
+  }
+
+More info about this command can be found in the `npm-test documentation https://docs.npmjs.com/cli/test`_.
+
+npm run lint (optional)
+-----------------------
+
+Nextcloud apps that use linting tools for consistent code formatting typically add a ``lint`` script to their
+``package.json``:
+
+.. code-block:: json
+
+  {
+    "scripts": {
+      "lint": "eslint --ext .js,.vue src"
+    }
+  }
+
+If style linting is a separate script, ``stylelint`` shall be used as conventional script name:
+
+.. code-block:: json
+
+  {
+    "scripts": {
+      "stylelint": "stylelint src"
+    }
+  }