There was a typo error in index.html file of day one.
@ -6,7 +6,7 @@
</head>
<body>
<h1>30DaysOfJavaScript:03 Day</h1>
<h1>30DaysOfJavaScript:01 Day</h1>
<h2>Introduction</h2>
<button onclick="alert('Welcome to 30DaysOfJavaScript!');">Click Me</button>
<script src="./helloworld.js"></script>
@ -16,4 +16,4 @@
</body>
</html>