gistfile1.js

[...]

var loadEmmet = true;
   
//one-time startup
var init = function() {
 aceConfig.themes.forEach(function(theme) {
   var option = document.createElement("option");
   option.innerHTML = theme.label;
   option.setAttribute("value", theme.name);
   themes.append(option);
 });

 if(loadEmmet) {
   //we need ace.lib.net to call loadScript, we can't just require Emmet and ask it to load itself
   //remember that ace.require is basically a sync version of RequireJS.
   ace.require("ace/lib/net").loadScript("js/ace/ext-emmet.js", function() {
     editor.session.setMode("ace/mode/html");
     editor.setOption("enableEmmet", true);  
   });
 }

 if (userConfig.emulateVim) {
   ace.require("ace/lib/net").loadScript("js/ace/keybinding-vim.js", function() {
     editor.setKeyboardHandler(ace.require("ace/keyboard/vim").handler);
   });
 }
 reset();
};

[...]