Run eslint on the scripts directory

I noticed that the `scripts` directory, which begins to have a lot of
files as we automate more tasks (like #1524), wasn't linted.

That directory contains code in two languages BASH and JS (Node.js),
with a move to prefer JS files (as it's a JS/TS project).

So I chose to add an `.eslintrc.js` file (which is a deprecated format
but I couldn't make the new one work) and lint script on that
directory.

I subsequently fixed some linting errors.

For now, that script isn't run by our GitHub actions, I will see whether
we can do an intelligent kind of runner which detects if scripts have
been updated.

demo/.eslintrc.js

@@ -3,8 +3,6 @@ module.exports = {
   env: {
     es6: true,
     browser: true,
-    commonjs: true,
-    mocha: true,
   },
 
   globals: {

package.json

@@ -151,7 +151,7 @@
     "bundle:watch": "./scripts/run_bundler.mjs src/index.ts --production-mode -o dist/rx-player.js --watch",
     "certificate": "./scripts/generate_certificate",
     "check": "npm run check:types && npm run lint && npm run check:types:unit_tests",
-    "check:all": "npm run check:types && npm run lint && npm run lint:demo && npm run lint:tests && npm run test:unit && npm run test:integration && npm run test:memory && node -r esm ./scripts/check_nodejs_import_compatibility.js",
+    "check:all": "npm run check:types && npm run lint && npm run lint:demo && npm run lint:tests && npm run lint:scripts && npm run test:unit && npm run test:integration && npm run test:memory && node -r esm ./scripts/check_nodejs_import_compatibility.js",
     "check:demo": "npm run check:demo:types && npm run lint:demo",
     "check:demo:types": "tsc --noEmit --project demo/",
     "clean:build": "scripts/remove_dir.mjs dist",
@@ -169,6 +169,7 @@
     "fmt:rust:check": "cd ./src/parsers/manifest/dash/wasm-parser && cargo fmt --check",
     "lint": "eslint src -c .eslintrc.js",
     "lint:demo": "eslint -c demo/.eslintrc.js demo/scripts",
+    "lint:scripts": "eslint -c scripts/.eslintrc.js --ext .js --ext .mjs --ext .cjs scripts",
     "lint:tests": "eslint tests/**/*.js --ignore-pattern '/tests/performance/bundle*'",
     "list": "node scripts/list-npm-scripts.mjs",
     "prepublishOnly": "npm run build:all",

scripts/run_bundler.mjs

@@ -62,16 +62,18 @@ if (import.meta.url === pathToFileURL(process.argv[1]).href) {
   }
 
   try {
-    await runBundler(normalizedPath, {
+    runBundler(normalizedPath, {
       watch: shouldWatch,
       minify: shouldMinify,
       production,
       silent,
       outfile,
+    }).catch((err) => {
+      console.error(`ERROR: ${err}\n`);
+      process.exit(1);
     });
   } catch (err) {
     console.error(`ERROR: ${err}\n`);
-    displayHelp();
     process.exit(1);
   }
 }