Use toString where JSON.stringify didn't work

crates/cli-support/src/js/mod.rs

@@ -350,6 +350,23 @@ impl<'a> Context<'a> {
             ))
         })?;
 
+        self.bind("__wbindgen_to_string", &|me| {
+            me.expose_pass_string_to_wasm()?;
+            me.expose_get_object();
+            me.expose_uint32_memory();
+            Ok(String::from(
+                "
+                function(i, len_ptr) {
+                    let toString = getObject(i).toString();
+                    if (typeof(toString) !== 'string') return 0;
+                    const ptr = passStringToWasm(toString);
+                    getUint32Memory()[len_ptr / 4] = WASM_VECTOR_LEN;
+                    return ptr;
+                }
+                ",
+            ))
+        })?;
+
         self.bind("__wbindgen_cb_drop", &|me| {
             me.expose_drop_ref();
             Ok(String::from(

src/lib.rs

@@ -313,6 +313,21 @@ impl JsValue {
             String::from_utf8_unchecked(s)
         }
     }
+
+    /// Get the string value of self using the JS `toString` method.
+    #[cfg(feature = "std")]
+    fn js_to_string(&self) -> String {
+        unsafe {
+            let mut len = 0;
+            let ptr = __wbindgen_to_string(self.idx, &mut len);
+            if ptr.is_null() {
+                unreachable!("Object.toString must return a valid string")
+            } else {
+                let data = Vec::from_raw_parts(ptr, len, len);
+                String::from_utf8_unchecked(data)
+            }
+        }
+    }
 }
 
 impl PartialEq for JsValue {
@@ -488,6 +503,7 @@ externs! {
     fn __wbindgen_is_function(idx: u32) -> u32;
     fn __wbindgen_is_string(idx: u32) -> u32;
     fn __wbindgen_string_get(idx: u32, len: *mut usize) -> *mut u8;
+    fn __wbindgen_to_string(idx: u32, len: *mut usize) -> *mut u8;
     fn __wbindgen_throw(a: *const u8, b: usize) -> !;
     fn __wbindgen_rethrow(a: u32) -> !;
 
@@ -539,7 +555,7 @@ impl fmt::Debug for JsValue {
         }
         let json = self.as_json();
         if json == "{}" {
-            f.write_str("[object]")
+            f.write_str(&self.js_to_string())
         } else {
             f.write_str(&json)
         }