Plugin checks API version

src/main/webapp/myPlugins/dtdesign.js

@@ -1,4 +1,5 @@
 const BACKEND = "http://localhost:5000";
+const EXPECTED_BACKEND_VERSION = 1; // expected backend version
 const SPARQL_SERVER   = "http://localhost:3030"
 const SPARQL_ENDPOINT = "/SystemDesignOntology2Layers/sparql"
 
@@ -120,6 +121,20 @@ const defaultSettings = {
 
 Draw.loadPlugin(function(ui) {
 
+fetch(BACKEND+"/version")
+.then(response => response.json())
+.catch(() => 0) // parsing failed - probably backend doesn't even have a version
+.then(version => {
+
+  if (version != EXPECTED_BACKEND_VERSION) {
+    alert("Incorrect DTDesign Python backend version.\nExpected: " + EXPECTED_BACKEND_VERSION + ", got: " + version + ".\nRefusing to load plugin. Please upgrade :)");
+    return;
+  }
+  else {
+    console.log("Backend version is ", version);
+    console.log("All good.")
+  }
+
   executeSPARQL(getSubClassRelations)
   .then(results => {
     for (const {subclass, superclass} of results) {
@@ -484,4 +499,6 @@ Draw.loadPlugin(function(ui) {
     })
 
   wnd.show();
+
+}) // end of promise that checks the backend version.
 })