javascript code - function in function

i am trying to understand this code-
in this code, a function is written inside a function -

   <script>
 
      require([
        "esri/map", "esri/layers/ArcGISTiledMapServiceLayer", 
        "esri/domUtils", "esri/request",
        "dojo/parser", "dojo/number", "dojo/json", "dojo/dom", 
        "dijit/registry", "modules/RasterLayer",

        "dijit/layout/BorderContainer", "dijit/layout/ContentPane", 
        "dijit/form/HorizontalSlider", "dojo/domReady!"
      ], function(
        Map, ArcGISTiledMapServiceLayer, 
        domUtils, esriRequest,
        parser, number, JSON, dom, 
        registry, RasterLayer
      ) {

        //some code 
        function mapLoaded() {
//code of maploaded
        }

        function getRasterData() {
       //code 
        }

        function setElevation() {
        //code 
         }
 
         function supports_canvas() {
                //code 
         }
      });
    </script>

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Why the functions "setElevation()", "supports_canvas()", "getRasterData() ",  "mapLoaded()"  
are written within
 thanks so much

pl guide