src/app/index.html

<!DOCTYPE html>
<html>
    <head>
        <title>esri-webpack-demo</title>
        <!--esri styles are loaded outside of webpack-->
        <link rel="stylesheet" href="https://js.arcgis.com/3.18/esri/css/esri.css">
        <style>
        html, body, #content {
            padding: 0;
            margin: 0;
            height: 100%;
            width: 100%;
        }
        </style>
    </head>

    <body>
        <div id="content"></div>
        <!-- optionally configure Dojo loader before loading the ArcGIS API for JavaScript -->
        <script>
          window.dojoConfig = {
            async: true,
            // in this example we're using a third party library 
            // that is not bundled with the ArcIGS API for JavaScript
            // so we need to tell Dojo where to load it from
            packages: [{
              name: 'cluster-layer-js',
              location: '//rawgit.com/Esri/cluster-layer-js/master/src'
            }]
          };
        </script>
        <!-- the ArcGIS API for JavaScript must be loaded outside of webpack-->
        <script src="https://js.arcgis.com/3.18/"></script>
        <script>
            // once the ArcGIS API for JavaScript has loaded
            // we must use Dojo's require() to load the bundled webpack output
            // only the Dojo loader will be able to resolve the bundle's references
            // to "external" dependencies on modules in the esri and dojo packages
            require(["../../dist/vendor.bundle.js", "../../dist/main.bundle.js"], function (vendor, main) {});
        </script>
    </body>
</html>