eslint: Enable no-var rule

`var` has broken/unexpected scoping in JavaScript, and can lead to
subtle errors. It's preferable and safer to use `const` whenever
possible, and `let` where necessary.

Most pages got updated by now, so let's make sure they stay that way.
Disable the rule for the four remaining known pages which still use
`var`. Also temporarily downgrade the `error` to `warn` when running
`npm run eslint`, as that is covered by the unit-tests "distcheck"
scenario. This requires touching package.json and thus a node_modules
rebuild.

.eslintrc.json

@@ -25,6 +25,7 @@
         "newline-per-chained-call": ["error", { "ignoreChainWithDepth": 2 }],
         "lines-between-class-members": ["error", "always", { "exceptAfterSingleLine": true }],
         "prefer-promise-reject-errors": ["error", { "allowEmptyReject": true }],
+        "no-var": "error",
         "react/jsx-indent": ["error", 4],
         "semi": ["error", "always", { "omitLastInOneLineBlock": true }],
 

package.json

@@ -74,7 +74,7 @@
     "webpack-cli": "^4.7.0"
   },
   "scripts": {
-    "eslint": "eslint --ext .js --ext .jsx pkg/",
+    "eslint": "eslint --ext .js --ext .jsx pkg/ --rule 'no-var: warn'",
     "eslint:fix": "eslint --fix --ext .js --ext .jsx pkg/"
   }
 }

webpack.config.js

@@ -351,8 +351,13 @@ const plugins = [
     }),
 ];
 
-if (eslint)
-    plugins.push(new ESLintPlugin({ extensions: ["js", "jsx"] }));
+if (eslint) {
+    // temporary hack: not all pages got converted to no-var yet; drop this again once they are
+    const overrideConfig = {};
+    if (section === "shell/" || section === 'networkmanager/' || section === "static/" || section === "systemd/")
+        overrideConfig.rules = { "no-var": "off" };
+    plugins.push(new ESLintPlugin({ extensions: ["js", "jsx"], overrideConfig }));
+}
 
 if (section.startsWith('base1'))
     plugins.push(new copy({ patterns: base1_fonts }));