init: it builds

um_wasm/src/lib.rs

@@ -0,0 +1,19 @@
+mod utils;
+
+use utils::set_panic_hook;
+use wasm_bindgen::prelude::*;
+
+#[wasm_bindgen]
+extern "C" {
+    fn alert(s: &str);
+}
+
+#[wasm_bindgen]
+pub fn init() {
+    set_panic_hook();
+}
+
+#[wasm_bindgen]
+pub fn greet() {
+    alert("hello world!");
+}

um_wasm/src/utils.rs

@@ -0,0 +1,10 @@
+pub fn set_panic_hook() {
+    // When the `console_error_panic_hook` feature is enabled, we can call the
+    // `set_panic_hook` function at least once during initialization, and then
+    // we will get better error messages if our code ever panics.
+    //
+    // For more details see
+    // https://github.com/rustwasm/console_error_panic_hook#readme
+    #[cfg(feature = "console_error_panic_hook")]
+    console_error_panic_hook::set_once();
+}