Line Crossing the Date Line

Using unwrapped coordinates to cross the line
<!DOCTYPE html>
<html>
<head>
<meta charset=utf-8 />
<title>Line Crossing the Date Line</title>
  <meta name='viewport' content='width=device-width, initial-scale=1.0, maximum-scale=1.0, user-scalable=no' />
  <script src='//api.tiles.mapbox.com/mapbox.js/v1.4.0/mapbox.js'></script>
  <link href='//api.tiles.mapbox.com/mapbox.js/v1.4.0/mapbox.css' rel='stylesheet' />
  <!--[if lte IE 8]>
    <link href='//api.tiles.mapbox.com/mapbox.js/v1.4.0/mapbox.ie.css' rel='stylesheet'>
  <![endif]-->
  <style>
    body { margin:0; padding:0; }
    #map { position:absolute; top:0; bottom:0; width:100%; }
  </style>
</head>
<body>
<div id='map'></div>
<script type='text/javascript'>
var map = L.mapbox.map('map', 'examples.map-20v6611k')
    .setView([37.9, -77], 6);

L.geoJson({
    type: 'Feature',
    geometry: {
        type: 'LineString',
        // the coordinate -233.9 is technically invalid but Leaflet
        // permits it because it can imply the direction of wrapping -
        // to wrap in a direction, you can add or subtract 360 from
        // the desired end coordinate
        coordinates: [[-77, 37.9], [-233.9, 36.5]]
    },
    properties: { }
}).addTo(map);
</script>
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