Edit in JSFiddle

JavaScript
HTML
CSS
Result

function initialize()
{
    var map = new google.maps.Map(document.getElementById("map_canvas"),
    {
        zoom: 4,
              center: new google.maps.LatLng(20.632784,78.969727),
              mapTypeId: google.maps.MapTypeId.ROADMAP   
    });

    var route = [
                new google.maps.LatLng(22.568049,88.322868), //Kolkata
                new google.maps.LatLng(28.639979,77.233887), //New Delhi
                new google.maps.LatLng(12.98181,77.578239),   //Bengaluru
                new google.maps.LatLng(18.958246,73.053589)  //Mumbai
        ];

    var path = new google.maps.Polyline(
    {
              path: route,
              strokeColor: "#FF0000",
              strokeOpacity: 1.0,
              strokeWeight: 2
        });
    path.setMap(map);
}

<html>
<head>
<title>Google Maps API v3 : Hardcoded Polyline</title>
<script type="text/javascript" src="http://maps.google.com/maps/api/js?sensor=false"></script>
<script type="text/javascript">
</script>
</head>
<body onload="initialize()">
<div id="map_canvas" style="width:530px; height:230px">
</div>
</body>
</html>