RequireJS

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Metro UI CSS now support using AMD. This means that you can load Metro UI Javascript library asynchronously using an AMD loader such as RequireJS.
HTML

                <!DOCTYPE html>
                <html lang="en">
                <head>
                    <meta charset="UTF-8">
                    <title>Metro UI CSS with RequireJS</title>

                    <link href="css/metro.min.css" rel="stylesheet">

                    <script data-main="scripts/main" src="scripts/require.js"></script>
                </head>
JS (main.js)

                require.config({
                    paths: {
                        jquery: "jquery",
                        metro: "metro"
                    },
                    shim: {
                        metro: {
                            deps: ['jquery']
                        }
                    }
                });

                require(
                    ["jquery", "metro"],
                    function($){
                        ... put you code ...
                    }
                );
JS with others (main.js + underscore + backbone)

                require.config({
                    paths: {
                        jquery: "jquery",
                        underscore: "underscore",
                        backbone: "backbone",
                        metro: "metro"
                    },

                    shim: {
                        underscore: {
                            exports: '_'
                        },
                        backbone: {
                            deps: ["underscore", "jquery"],
                            exports: "Backbone"
                        },
                        metro: {
                            deps: ['jquery']
                        }
                    }
                });

                require(
                    ["jquery", "underscore", "backbone", "metro"],
                    function($, _, Backbone){
                        ... put you code ...
                    }
                );