Events now fire synchronously

In the JavaScript package loro-crdt@1.8.0, we changed event emission from “after a microtask” to synchronous dispatch. This makes event handling simpler and less error‑prone.

Why we changed it

Historically, the JS binding emitted events after a microtask. The reason was to avoid Rust borrow/aliasing issues: if an event triggered inside doc.commit() re‑entered the same doc, Rust could panic because commit() holds a borrow and reusing the object would violate borrowing rules. Deferring events to a microtask avoided that re‑entrancy. (Background: Loro’s JS API exposes subscriptions via doc.subscribe(...); the docs note that events used to arrive after a microtask. ([Loro][1]))

However, this deferral made app logic fragile. There was a window between the mutation and the event callback. Example: the app receives the event from CRDT “delete the 3rd character of Hi!”, but during the microtask gap the app state changed Hi! → Hi. When the deferred event arrives, applying a “delete index 2” delta can be wrong. In practice, users had to maintain an awkward invariant: don’t mutate the app state during that microtask if you consume delta updates.

What’s new in 1.8.0

Events are now dispatched synchronously—that is, your listeners run before the top‑level JS call (e.g., doc.commit()) returns. To keep this safe with Rust’s borrowing:

• We keep a global queue of “pending (listener, event)” pairs.
• JS wrappers decorate APIs that can borrow the Rust doc (e.g., commit, import/export, checkout).
• The wrapper calls into WASM/Rust, returns from the borrow, then flushes the queue and clears it.
• Because callbacks run outside the borrowed region, listeners can freely call doc APIs without triggering borrow violations.

What this means for your app

• Simpler state updates. No more microtask gap; event ordering matches your mutation order.
• Fewer footguns with deltas. You no longer need to uphold “don’t touch the doc during the microtask” when applying delta‑style updates.
• Listeners can still safely use doc.