![]() ![]() IndexedDB uses the standard serialization algorithm to clone-and-store an object. We can store almost any value, including complex objects. A database may have multiple stores: one for users, another one for goods, etc.ĭespite being named an “object store”, primitives can be stored too. Counterparts in other databases are called “tables” or “collections”. To store something in IndexedDB, we need an object store.Īn object store is a core concept of IndexedDB. These update collisions happen rarely, but we should at least have some handling for them, at least an onblocked handler, to prevent our script from dying silently. Or, an alternative approach would be to not close the database in db.onversionchange, but instead use the onblocked handler (in the new tab) to alert the visitor, tell him that the newer version can’t be loaded until they close other tabs. We can handle things more gracefully in db.onversionchange, prompt the visitor to save the data before the connection is closed and so on. The openRequest.onblocked listener informs us about the opposite situation: there’s a connection to an outdated version elsewhere, and it doesn’t close, so the newer connection can’t be made.The db.onversionchange listener informs us about a parallel update attempt, if the current database version becomes outdated.and it wasn't closed after db.onversionchange triggered for it it means that there's another open connection to the same database this event shouldn't trigger if we handle onversionchange correctly Let openRequest = indexedDB.open("store", 2) Īlert("Database is outdated, please reload the page.") ![]() It installs the onversionchange handler, that triggers if the current database connection becomes outdated (db version is updated elsewhere) and closes the connection. Here’s the code to correctly handle the parallel upgrade. The openRequest object will emit the blocked event instead of success. If we don’t listen for the versionchange event and don’t close the old connection, then the second, new connection won’t be made. We should listen for it and close the old database connection (and probably suggest a page reload, to load the updated code). In order to organize that, the versionchange event triggers on the “outdated” database object. To perform the update to version 2, all connections to version 1 must be closed, including the one in the first tab. The problem is that a database is shared between two tabs, as it’s the same site, same origin. So there’s a tab with an open connection to DB version 1, while the second one attempts to update it to version 2 in its upgradeneeded handler. And then the same visitor opens our site in another tab.Then we rolled out an update, so our code is newer.A visitor opened our site in a browser tab, with database version 1.Parallel update problemĪs we’re talking about versioning, let’s tackle a small related problem. Use proper HTTP caching headers to avoid loading the old code, so that you’ll never have such problems. To protect from errors, we should check db.version and suggest a page reload. So the code is old, but his database is new. That’s rare, but such a thing may happen when a visitor loads outdated JavaScript code, e.g. the existing DB version is 3, and we try to open(.2), then that’s an error, openRequest.onerror triggers. If the current user database has a higher version than in the open call, e.g. Then we can open the database with version 1 and perform the initialization in an upgradeneeded handler like this: Let’s say we published the first version of our app. The upgradeneeded event also triggers when the database doesn’t yet exist (technically, its version is 0), so we can perform the initialization. If the local database version is less than specified in open, then a special event upgradeneeded is triggered, and we can compare versions and upgrade data structures as needed. So, when we have published a new version of our app, and the user visits our webpage, we may need to update the database. Unlike server-side databases, IndexedDB is client-side, the data is stored in the browser, so we, developers, don’t have full-time access to it. IndexedDB has a built-in mechanism of “schema versioning”, absent in server-side databases. upgradeneeded: database is ready, but its version is outdated (see below).success: database is ready, there’s the “database object” in openRequest.result, we should use it for further calls.The call returns openRequest object, we should listen to events on it: Different websites can’t access each other’s databases. We can have many databases with different names, but all of them exist within the current origin (domain/protocol/port). version – a positive integer version, by default 1 (explained below).Let openRequest = indexedDB.open(name, version) ![]()
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