How to reference the ArcGIS Server JS API using RequireJS

You would do this

requirejs.config({
  'paths': {
    'esri': 'http://js.arcgis.com/3.12/esri',
    'dojo': 'http://js.arcgis.com/3.12/dojo',
    'dojox': 'http://js.arcgis.com/3.12/dojox',
    'dijit': 'http://js.arcgis.com/3.12/dijit'
  }
});

Then require your modules in AMD style like this

requirejs(["esri/dijit/BasemapGallery", 
         "dojo/dom", 
         "dijit/form/Button", 
         "dojox/grid/DataGrid"], 
         function(BasemapGallery, dom, Button, DataGrid){
});