index.js

let db;
let version = 1;
const request = indexedDB.open("database", version);
request.onerror = function(event) {
  alert("IndexedDB が使えません");
};
request.onupgradeneeded = function(event) {
  db = event.target.result;
  const objectStore = db.createObjectStore("items", { keyPath: "id" });
  objectStore.createIndex("name", "name", { unique: false });
  objectStore.createIndex("description", "description", { unique: true });
};
request.onsuccess = function(event) {
  db = event.target.result;
}