Calling console.log from rust wasm32-wasi without the need for ssvm/ssvmup

Question

I would like to debug using messages to the console.log.

We have a rust wasm32-wasi function being called from javascript running in nodejs. We can not use ssvm/ssvmup due to other restrictions.

Is there anything we can do to see messages from our wasm code in the console?

Answer 1

This is answered in The wasm-bindgen Guide: Using console.log:

• Method #1, binding it manually:

  #[wasm_bindgen]
  extern "C" {
      // Use `js_namespace` here to bind `console.log(..)` instead of just
      // `log(..)`
      #[wasm_bindgen(js_namespace = console)]
      fn log(s: &str);
  
      // The `console.log` is quite polymorphic, so we can bind it with multiple
      // signatures. Note that we need to use `js_name` to ensure we always call
      // `log` in JS.
      #[wasm_bindgen(js_namespace = console, js_name = log)]
      fn log_u32(a: u32);
  
      // Multiple arguments too!
      #[wasm_bindgen(js_namespace = console, js_name = log)]
      fn log_many(a: &str, b: &str);
  }
  
  fn bare_bones() {
      log("Hello from Rust!");
      log_u32(42);
      log_many("Logging", "many values!");
  }
  

• Method #2, using the web-sys crate:

  fn using_web_sys() {
      use web_sys::console;
  
      console::log_1(&"Hello using web-sys".into());
  
      let js: JsValue = 4.into();
      console::log_2(&"Logging arbitrary values looks like".into(), &js);
  }
  

Another potential alternative, if you're doing a lot of logging you may want to consider using the log crate with the wasm-logger facade:

wasm_logger::init(wasm_logger::Config::default());

// Logging
log::info!("Some info");
log::error!("Error message");