Using Razor within JavaScript

What specific errors are you seeing?

Something like this could work better:

<script type="text/javascript">

//now add markers
 @foreach (var item in Model) {
    <text>
      var markerlatLng = new google.maps.LatLng(@Model.Latitude, @Model.Longitude);
      var title = '@(Model.Title)';
      var description = '@(Model.Description)';
      var contentString = '<h3>' + title + '</h3>' + '<p>' + description + '</p>'
    </text>
}
</script>

Note that you need the magical <text> tag after the foreach to indicate that Razor should switch into markup mode.

I just wrote this helper function. Put it in App_Code/JS.cshtml:

@using System.Web.Script.Serialization
@helper Encode(object obj)
{
    @(new HtmlString(new JavaScriptSerializer().Serialize(obj)));
}

Then in your example, you can do something like this:

var title = @JS.Encode(Model.Title);

Notice how I don't put quotes around it. If the title already contains quotes, it won't explode. Seems to handle dictionaries and anonymous objects nicely too!

You're trying to jam a square peg in a round hole.

Razor was intended as an HTML-generating template language. You may very well get it to generate JavaScript code, but it wasn't designed for that.

For instance: What if Model.Title contains an apostrophe? That would break your JavaScript code, and Razor won't escape it correctly by default.

It would probably be more appropriate to use a String generator in a helper function. There will likely be fewer unintended consequences of that approach.

Use the <text> pseudo-element, as described here, to force the Razor compiler back into content mode:

<script type="text/javascript">

    // Some JavaScript code here to display map, etc.


    // Now add markers
    @foreach (var item in Model) {
        <text>
            var markerlatLng = new google.maps.LatLng(@(Model.Latitude), @(Model.Longitude));
            var title = '@(Model.Title)';
            var description = '@(Model.Description)';
            var contentString = '<h3>' + title + '</h3>' + '<p>' + description + '</p>'

            var infowindow = new google.maps.InfoWindow({
                content: contentString
            });

            var marker = new google.maps.Marker({
                position: latLng,
                title: title,
                map: map,
                draggable: false
            });

            google.maps.event.addListener(marker, 'click', function () {
                infowindow.open(map, marker);
            });
        </text>
    }
</script>

Update:

Scott Guthrie recently posted about @: syntax in Razor, which is slightly less clunky than the <text> tag if you just have one or two lines of JavaScript code to add. The following approach would probably be preferable, because it reduces the size of the generated HTML. (You could even move the addMarker function to a static, cached JavaScript file to further reduce the size):

<script type="text/javascript">

    // Some JavaScript code here to display map, etc.
    ...
    // Declare addMarker function
    function addMarker(latitude, longitude, title, description, map)
    {
        var latLng = new google.maps.LatLng(latitude, longitude);
        var contentString = '<h3>' + title + '</h3>' + '<p>' + description + '</p>';

        var infowindow = new google.maps.InfoWindow({
            content: contentString
        });

        var marker = new google.maps.Marker({
            position: latLng,
            title: title,
            map: map,
            draggable: false
        });

        google.maps.event.addListener(marker, 'click', function () {
            infowindow.open(map, marker);
        });
    }

    // Now add markers
    @foreach (var item in Model) {
        @:addMarker(@item.Latitude, @item.Longitude, '@item.Title', '@item.Description', map);
    }
</script>

Updated the above code to make the call to addMarker more correct.

To clarify, the @: forces Razor back into text mode, even though addMarker call looks a lot like C# code. Razor then picks up the @item.Property syntax to say that it should directly output the contents of those properties.

Update 2

It's worth noting that View code really isn't a good place to put JavaScript code. JavaScript code should be placed in a static .js file, and then it should get the data that it needs either from an Ajax call or by scanning data- attributes from the HTML. Besides making it possible to cache your JavaScript code, this also avoids issues with encoding, since Razor is designed to encode for HTML, but not JavaScript.

View Code

@foreach(var item in Model)
{
    <div data-marker="@Json.Encode(item)"></div>
}

JavaScript code

$('[data-marker]').each(function() {
    var markerData = $(this).data('marker');
    addMarker(markerData.Latitude, markerData.Longitude,
              markerData.Description, markerData.Title);
});