Fix WASM playground (#2992)

Cargo.lock

@@ -604,6 +604,7 @@ version = "0.16.0"
 dependencies = [
  "boa_engine",
  "chrono",
+ "console_error_panic_hook",
  "getrandom",
  "wasm-bindgen",
 ]
@@ -936,6 +937,16 @@ dependencies = [
  "windows-sys 0.42.0",
 ]
 
+[[package]]
+name = "console_error_panic_hook"
+version = "0.1.7"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a06aeb73f470f66dcdbf7223caeebb85984942f22f1adb2a088cf9668146bbbc"
+dependencies = [
+ "cfg-if 1.0.0",
+ "wasm-bindgen",
+]
+
 [[package]]
 name = "const_fn"
 version = "0.4.9"

boa_engine/src/context/mod.rs

@@ -20,7 +20,7 @@ use crate::{
     builtins,
     class::{Class, ClassBuilder},
     job::{JobQueue, NativeJob, SimpleJobQueue},
-    module::{ModuleLoader, SimpleModuleLoader},
+    module::{IdleModuleLoader, ModuleLoader, SimpleModuleLoader},
     native_function::NativeFunction,
     object::{shape::RootShape, FunctionObjectBuilder, JsObject},
     optimizer::{Optimizer, OptimizerOptions, OptimizerStatistics},
@@ -873,6 +873,21 @@ impl<'icu, 'hooks, 'queue, 'module> ContextBuilder<'icu, 'hooks, 'queue, 'module
         let realm = Realm::create(&*host_hooks, &root_shape);
         let vm = Vm::new(realm.environment().clone());
 
+        let module_loader = if let Some(loader) = self.module_loader {
+            loader
+        } else {
+            SimpleModuleLoader::new(Path::new(".")).map_or_else(
+                |_| {
+                    let loader: &dyn ModuleLoader = &IdleModuleLoader;
+                    loader.into()
+                },
+                |loader| {
+                    let loader: Rc<dyn ModuleLoader> = Rc::new(loader);
+                    loader.into()
+                },
+            )
+        };
+
         let mut context = Context {
             realm,
             interner: self.interner.unwrap_or_default(),
@@ -892,13 +907,7 @@ impl<'icu, 'hooks, 'queue, 'module> ContextBuilder<'icu, 'hooks, 'queue, 'module
                 let queue: Rc<dyn JobQueue> = Rc::new(SimpleJobQueue::new());
                 queue.into()
             }),
-            module_loader: self.module_loader.unwrap_or_else(|| {
-                let loader: Rc<dyn ModuleLoader> = Rc::new(
-                    SimpleModuleLoader::new(Path::new("."))
-                        .expect("failed to initialize default module loader"),
-                );
-                loader.into()
-            }),
+            module_loader,
             optimizer_options: OptimizerOptions::OPTIMIZE_ALL,
             root_shape,
             parser_identifier: 0,

boa_engine/src/module/mod.rs

@@ -129,6 +129,29 @@ pub trait ModuleLoader {
     }
 }
 
+/// A module loader that throws when trying to load any modules.
+///
+/// Useful to disable the module system on platforms that don't have a filesystem, for example.
+#[derive(Debug, Clone, Copy)]
+pub struct IdleModuleLoader;
+
+impl ModuleLoader for IdleModuleLoader {
+    fn load_imported_module(
+        &self,
+        _referrer: Referrer,
+        _specifier: JsString,
+        finish_load: Box<dyn FnOnce(JsResult<Module>, &mut Context<'_>)>,
+        context: &mut Context<'_>,
+    ) {
+        finish_load(
+            Err(JsNativeError::typ()
+                .with_message("module resolution is disabled for this context")
+                .into()),
+            context,
+        );
+    }
+}
+
 /// A simple module loader that loads modules relative to a root path.
 #[derive(Debug)]
 pub struct SimpleModuleLoader {
@@ -139,6 +162,11 @@ pub struct SimpleModuleLoader {
 impl SimpleModuleLoader {
     /// Creates a new `SimpleModuleLoader` from a root module path.
     pub fn new<P: AsRef<Path>>(root: P) -> JsResult<Self> {
+        if cfg!(target_family = "wasm") {
+            return Err(JsNativeError::typ()
+                .with_message("cannot resolve a relative path in WASM targets")
+                .into());
+        }
         let root = root.as_ref();
         let absolute = root.canonicalize().map_err(|e| {
             JsNativeError::typ()

boa_wasm/Cargo.toml

@@ -16,6 +16,7 @@ boa_engine.workspace = true
 wasm-bindgen = "0.2.86"
 getrandom = { version = "0.2.9", features = ["js"] }
 chrono = { version = "0.4.26", features = ["clock", "std", "wasmbind"] }
+console_error_panic_hook = "0.1.7"
 
 [features]
 default = ["boa_engine/annex-b"]

boa_wasm/src/lib.rs

@@ -63,6 +63,11 @@ use chrono as _;
 use getrandom as _;
 use wasm_bindgen::prelude::*;
 
+#[wasm_bindgen(start)]
+fn main() {
+    console_error_panic_hook::set_once();
+}
+
 /// Evaluate the given ECMAScript code.
 #[wasm_bindgen]
 pub fn evaluate(src: &str) -> Result<String, JsValue> {