use prettier to fmt.

rollup.config.ts

@@ -1,11 +1,11 @@
-import svelte from 'rollup-plugin-svelte';
-import commonjs from '@rollup/plugin-commonjs';
-import resolve from '@rollup/plugin-node-resolve';
-import livereload from 'rollup-plugin-livereload';
-import { terser } from 'rollup-plugin-terser';
-import sveltePreprocess from 'svelte-preprocess';
-import typescript from '@rollup/plugin-typescript';
-import css from 'rollup-plugin-css-only';
+import svelte from "rollup-plugin-svelte";
+import commonjs from "@rollup/plugin-commonjs";
+import resolve from "@rollup/plugin-node-resolve";
+import livereload from "rollup-plugin-livereload";
+import { terser } from "rollup-plugin-terser";
+import sveltePreprocess from "svelte-preprocess";
+import typescript from "@rollup/plugin-typescript";
+import css from "rollup-plugin-css-only";
 
 const production = !process.env.ROLLUP_WATCH;
 
@@ -19,36 +19,40 @@ function serve() {
   return {
     writeBundle() {
       if (server) return;
-			server = require('child_process').spawn('npm', ['run', 'start', '--', '--dev'], {
+      server = require("child_process").spawn(
+        "npm",
+        ["run", "start", "--", "--dev"],
+        {
           // stdio: ['ignore', 'inherit', 'inherit'],
           // shell: true
-			});
-
-			process.on('SIGTERM', toExit);
-			process.on('exit', toExit);
         }
+      );
+
+      process.on("SIGTERM", toExit);
+      process.on("exit", toExit);
+    },
   };
 }
 
 export default {
-	input: 'src/main.ts',
+  input: "src/main.ts",
   output: {
     sourcemap: true,
-		format: 'iife',
-		name: 'app',
-		file: 'public/build/bundle.js'
+    format: "iife",
+    name: "app",
+    file: "public/build/bundle.js",
   },
   plugins: [
     svelte({
       preprocess: sveltePreprocess({ sourceMap: !production }),
       compilerOptions: {
         // enable run-time checks when not in production
-				dev: !production
-			}
+        dev: !production,
+      },
     }),
     // we'll extract any component CSS out into
     // a separate file - better for performance
-		css({ output: 'bundle.css' }),
+    css({ output: "bundle.css" }),
 
     // If you have external dependencies installed from
     // npm, you'll most likely need these plugins. In
@@ -57,13 +61,13 @@ export default {
     // https://github.com/rollup/plugins/tree/master/packages/commonjs
     resolve({
       browser: true,
-			dedupe: ['svelte']
+      dedupe: ["svelte"],
     }),
     commonjs(),
     typescript({
       sourceMap: true,
       //sourceMap: !production,
-			inlineSources: !production
+      inlineSources: !production,
     }),
 
     // In dev mode, call `npm run start` once
@@ -72,14 +76,14 @@ export default {
 
     // Watch the `public` directory and refresh the
     // browser on changes when not in production
-		!production && livereload('public'),
+    !production && livereload("public"),
 
     // If we're building for production (npm run build
     // instead of npm run dev), minify
-		production && terser()
+    production && terser(),
   ],
   watch: {
     buildDelay: 500,
-		clearScreen: false
-	}
+    clearScreen: false,
+  },
 };

src/main.ts

@@ -1,7 +1,7 @@
-import App from './App.svelte';
+import App from "./App.svelte";
 
 const app = new App({
-  target: document.body
+  target: document.body,
 });
 
 export default app;

src/util.js

@@ -1,8 +0,0 @@
-'use strict'
-
-export function sleep(ms) {
-  const p = new Promise((resolve, reject) => {
-    setTimeout(resolve, ms)
-  })
-  return p
-}

src/util.ts

@@ -0,0 +1,6 @@
+export function sleep(ms: number) {
+  const p = new Promise((resolve, reject) => {
+    setTimeout(resolve, ms);
+  });
+  return p;
+}