Mix Razor and Javascript code

Inside a code block (eg, @foreach), you need to mark the markup (or, in this case, Javascript) with @: or the <text> tag.

Inside the markup contexts, you need to surround code with code blocks (@{ ... } or @if, ...)

Use <text>:

<script type="text/javascript">

   var data = [];

   @foreach (var r in Model.rows)
   {
      <text>
            data.push([ @r.UnixTime * 1000, @r.Value ]);
      </text>
   }
</script>

you also can simply use

<script type="text/javascript">

   var data = [];

   @foreach (var r in Model.rows)
   {
       @:data.push([ @r.UnixTime * 1000, @r.Value ]);
   }
</script>

note @: