try computed

proj/map/asset/js/main.js

@@ -52,9 +52,20 @@ fetch(jsonurl)
 
 let vm = new Vue({
   el: '#root',
+  computed : {
+    db: function () {
+      const jsonurl = "https://ed.brz9.dev/proj/map/asset/json/db.json"
+      let jdb
+
+      fetch(jsonurl)
+        .then(res => res.json())
+        .then(data => jdb = data)
+
+      return jdb
+    },
+  },
   data: {
     currentLang: 'fr',
-    db : jdb.db,
     db2 : {
       restaurants : {
         id : "resto",