refactor(es modules): modulize utils

src/scripts/indexedDB.js

@@ -0,0 +1,50 @@
+// indexedDB support: ldb object
+
+// @ts-ignore unimplemented historical interfaces
+const indexedDBfactory = window.indexedDB || window.mozIndexedDB || window.webkitIndexedDB || window.msIndexedDB;
+if (!indexedDBfactory) console.error("indexedDB not supported");
+
+let database;
+const databaseRequest = indexedDBfactory.open("d2", 1);
+
+databaseRequest.onsuccess = function () {
+  database = this.result;
+};
+
+databaseRequest.onerror = function (e) {
+  console.error("indexedDB request error", e);
+};
+
+databaseRequest.onupgradeneeded = function (event) {
+  database = null;
+  const store = databaseRequest.result.createObjectStore("s", {keyPath: "k"});
+  store.transaction.oncomplete = function (e) {
+    database = e.target.db;
+  };
+};
+
+function getValue(key, callback) {
+  if (!database) {
+    setTimeout(() => getValue(key, callback), 100);
+    return;
+  }
+
+  database.transaction("s").objectStore("s").get(key).onsuccess = function (e) {
+    const value = (e.target.result && e.target.result.v) || null;
+    callback(value);
+  };
+}
+
+function setValue(key) {
+  if (!database) {
+    setTimeout(() => setValue(key, value), 100);
+    return;
+  }
+
+  database
+    .transaction("s", "readwrite")
+    .objectStore("s")
+    .put({[key]: value});
+}
+
+export const ldb = {get: getValue, set: setValue};