removeAttribute()

js/script.js

function funMake() {
document.getElementById('p1').removeAttribute('style');
}

function funMake() {
document.getElementById('p1').removeAttribute('style');
}

index.html

<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8" />
<title>New Page</title>
<script src="js/script.js"></script>
</head>
<body>
<p id="p1" style="color: red">Hello World!</p>
<script>
funMake();
</script>
</body>
</html>

<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8" />
<title>New Page</title>
<script src="js/script.js"></script>
</head>
<body>
<p id="p1" style="color: red">Hello World!</p>
<script>
funMake();
</script>
</body>
</html>