This crate lets you debug panics on wasm32-unknown-unknown by providing a panic hook that forwards panic messages to console.error.

When an error is reported with console.error, browser devtools and node.js will typically capture a stack trace and display it with the logged error message.

Without console_error_panic_hook you just get something like RuntimeError: Unreachable executed

Browser:

Node:

With this panic hook installed you will see the panic message

Browser:

Node:

There are two ways to install this panic hook.

First, you can set the hook yourself by calling std::panic::set_hook in some initialization function:

extern crate console_error_panic_hook;
use std::panic;
fn my_init_function() {
    panic::set_hook(Box::new(console_error_panic_hook::hook));
    // ...
}

Alternatively, use set_once on some common code path to ensure that set_hook is called, but only the one time. Under the hood, this uses std::sync::Once.

extern crate console_error_panic_hook;
struct MyBigThing;
impl MyBigThing {
    pub fn new() -> MyBigThing {
        console_error_panic_hook::set_once();
        MyBigThing
    }
}

Many browsers only capture the top 10 frames of a stack trace. In rust programs this is less likely to be enough. To see more frames, you can set the non-standard value Error.stackTraceLimit. For more information see the MDN Web Docs or v8 docs.