| # Support for Weak References |
| |
| By default wasm-bindgen does not use the [TC39 weak references |
| proposal](https://github.com/tc39/proposal-weakrefs). This proposal just |
| advanced to stage 4 at the time of this writing, but it will still stake some |
| time for support to percolate into all the major browsers. |
| |
| Without weak references your JS integration may be susceptible to memory leaks |
| in Rust, for example: |
| |
| * You could forget to call `.free()` on a JS object, leaving the Rust memory |
| allocated. |
| * Rust closures converted to JS values (the `Closure` type) may not be executed |
| and cleaned up. |
| * Rust closures have `Closure::{into_js_value,forget}` methods which explicitly |
| do not free the underlying memory. |
| |
| These issues are all solved with the weak references proposal in JS. The |
| `--weak-refs` flag to the `wasm-bindgen` CLI will enable usage of |
| `FinalizationRegistry` to ensure that all memory is cleaned up, regardless of |
| whether it's explicitly deallocated or not. Note that explicit deallocation |
| is always a possibility and supported, but if it's not called then memory will |
| still be automatically deallocated with the `--weak-refs` flag. |
