A logger that routes messages to the browser's console.

use log::Level;
fn main() {
    console_log::init_with_level(Level::Debug);

    info!("It works!");

    // ...
}

Rust's log levels map to the browser's console log in the following way.

The "color" feature adds styling to the log messages.

Cargo.toml

console_log = { version = "1", features = ["color"] }

The styled log messages will be rendered as follows:

Twiggy reports this library adding about 180Kb to the size of a minimal wasm binary in a debug build. If you want to avoid this, mark the library as optional and conditionally initialize it in your code for non-release builds.

Cargo.toml

[dependencies]
cfg-if = "0.1"
log = "0.4"
console_log = { version = "1", optional = true }

[features]
default = ["console_log"]

lib.rs

use wasm_bindgen::prelude::*;
use cfg_if::cfg_if;

cfg_if! {
    if #[cfg(feature = "console_log")] {
        fn init_log() {
            use log::Level;
            console_log::init_with_level(Level::Trace).expect("error initializing log");
        }
    } else {
        fn init_log() {}
    }
}

#[wasm_bindgen]
pub fn main() {
    init_log();
    // ...
}

The file and line number information associated with the log messages reports locations from the shims generated by wasm-bindgen, not the location of the logger call.

This project is licensed under either of

• Apache License, Version 2.0, (LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0)
• MIT license (LICENSE-MIT or http://opensource.org/licenses/MIT)

at your option.

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in this project by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.

• wasm-logger
• wasm-bindgen-console-logger
• fern (use with console_log::log)