This PR allows the user to pass an optional filename argument

gulpfile.js

@@ -4,6 +4,7 @@ const glob = require('glob')
 const yargs = require('yargs')
 const through = require('through2');
 const qunit = require('node-qunit-puppeteer')
+const path = require('path');
 
 const {rollup} = require('rollup')
 const terser = require('@rollup/plugin-terser')
@@ -20,10 +21,26 @@ const minify = require('gulp-clean-css')
 const connect = require('gulp-connect')
 const autoprefixer = require('gulp-autoprefixer')
 
-const root = yargs.argv.root || '.'
+
+let rawFileArg = yargs.argv.file;
+
+if (Array.isArray(rawFileArg)) {
+    rawFileArg = rawFileArg[rawFileArg.length - 1];
+}
+
+// 1. Set the server's root to the current working directory (which should be the reveal.js folder)
+const root = process.cwd();
+
+// 2. Calculate the absolute path to the file provided by the argument.
+const absoluteFilePath = path.resolve(rawFileArg || 'index.html');
+
+// 3. Calculate the path to the slide file *relative* to the server root (reveal.js folder).
+const presentationFile = path.relative(root, absoluteFilePath);
+
 const port = yargs.argv.port || 8000
 const host = yargs.argv.host || 'localhost'
 
+
 const cssLicense = `
 reveal.js ${pkg.version}
 ${pkg.homepage}
@@ -293,7 +310,7 @@ gulp.task('package', gulp.series(async () => {
 
 }))
 
-gulp.task('reload', () => gulp.src(['index.html'])
+gulp.task('reload', () => gulp.src([absoluteFilePath])
     .pipe(connect.reload()));
 
 gulp.task('serve', () => {
@@ -302,15 +319,15 @@ gulp.task('serve', () => {
         root: root,
         port: port,
         host: host,
+        index: presentationFile,
         livereload: true
     })
 
-    const slidesRoot = root.endsWith('/') ? root : root + '/'
-    gulp.watch([
-        slidesRoot + '**/*.html',
-        slidesRoot + '**/*.md',
-        `!${slidesRoot}**/node_modules/**`, // ignore node_modules
-    ], gulp.series('reload'))
+    const watchTargets = [
+        absoluteFilePath,
+    ];
+
+    gulp.watch(watchTargets, gulp.series('reload'))
 
     gulp.watch(['js/**'], gulp.series('js', 'reload', 'eslint'))