smoa/docs/web-scaffold/offline-queue.js

/**
 * Minimal IndexedDB queue for sync operations (optional extension).
 * Usage: queueSyncItem({ method, url, headers, body }); flushSyncQueue() when online.
 */
(function (global) {
  const DB_NAME = 'smoa_sync_queue';
  const STORE = 'pending';
  function openDb() {
    return new Promise(function (resolve, reject) {
      const r = indexedDB.open(DB_NAME, 1);
      r.onerror = function () { reject(r.error); };
      r.onupgradeneeded = function () {
        r.result.createObjectStore(STORE, { keyPath: 'id', autoIncrement: true });
      };
      r.onsuccess = function () { resolve(r.result); };
    });
  }
  global.queueSyncItem = function (item) {
    return openDb().then(function (db) {
      return new Promise(function (resolve, reject) {
        const tx = db.transaction(STORE, 'readwrite');
        tx.objectStore(STORE).add({ created: Date.now(), item: item });
        tx.oncomplete = function () { resolve(); };
        tx.onerror = function () { reject(tx.error); };
      });
    });
  };
  global.flushSyncQueue = function (fetchImpl) {
    var f = fetchImpl || fetch;
    return openDb().then(function (db) {
      return new Promise(function (resolve) {
        const tx = db.transaction(STORE, 'readonly');
        const req = tx.objectStore(STORE).getAll();
        req.onsuccess = function () {
          var rows = req.result || [];
          resolve(rows);
        };
      });
    }).then(function (rows) {
      return Promise.all(
        rows.map(function (row) {
          var it = row.item;
          return f(it.url, { method: it.method, headers: it.headers, body: it.body });
        })
      );
    });
  };
})(typeof window !== 'undefined' ? window : this);