With dart:js the following should work :
import 'dart:js' as js;
main() {
js.context.callMethod('require', [new js.JsArray.from(["esri/map",
"esri/dijit/HomeButton", "dojo/domReady!"]), (Map, HomeButton) {
var map = new js.JsObject(Map, ["map", new js.JsObject.jsify({
'center': [-56.049, 38.485],
'zoom': 3,
'basemap': "streets"
})]);
var home = new js.JsObject(HomeButton, [new js.JsObject.jsify({
map: map
}), "HomeButton"]);
home.callMethod('startup');
}]);
}