diff --git a/Cargo.toml b/Cargo.toml
index b4fd74cd1..8c4641ea2 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -14,7 +14,7 @@ js-component-bindgen = { path = "./crates/js-component-bindgen" }
 wit-component = { workspace = true }
 
 [build-dependencies]
-anyhow = "1.0.71"
+anyhow = { workspace = true }
 js-component-bindgen = { path = "./crates/js-component-bindgen" }
 wit-component = { workspace = true }
 
diff --git a/adapter.wasm b/adapter.wasm
new file mode 100644
index 000000000..0177c1742
Binary files /dev/null and b/adapter.wasm differ
diff --git a/bin/self_build.rs b/bin/self_build.rs
index 2633a70fb..cd0d8690d 100644
--- a/bin/self_build.rs
+++ b/bin/self_build.rs
@@ -19,6 +19,10 @@ fn main() -> Result<()> {
         encoder = encoder.adapter("wasi_snapshot_preview1", &adapter)?;
 
         let adapted_component = encoder.encode()?;
+        fs::create_dir_all(PathBuf::from("./obj"))?;
+        let mut component_path = PathBuf::from("./obj").join(&name);
+        component_path.set_extension("component.wasm");
+        fs::write(component_path, &adapted_component)?;
 
         let import_map = HashMap::from([
             (
diff --git a/crates/js-component-bindgen/src/intrinsics.rs b/crates/js-component-bindgen/src/intrinsics.rs
index de2eb51df..178192aae 100644
--- a/crates/js-component-bindgen/src/intrinsics.rs
+++ b/crates/js-component-bindgen/src/intrinsics.rs
@@ -116,10 +116,10 @@ pub fn render_intrinsics(
                 }
             "),
 
-            Intrinsic::DataView => output.push_str("
-                let dv = new DataView(new ArrayBuffer());
-                const dataView = mem => dv.buffer === mem.buffer ? dv : dv = new DataView(mem.buffer);
-            "),
+          Intrinsic::DataView => output.push_str("
+              let dv = new DataView(new ArrayBuffer());
+              const dataView = mem => dv.buffer === mem.buffer ? dv : dv = new DataView(mem.buffer);
+          "),
 
             Intrinsic::FetchCompile => if !no_nodejs_compat {
                 output.push_str("
diff --git a/crates/js-component-bindgen/src/transpile_bindgen.rs b/crates/js-component-bindgen/src/transpile_bindgen.rs
index aee5f715f..077a2f20d 100644
--- a/crates/js-component-bindgen/src/transpile_bindgen.rs
+++ b/crates/js-component-bindgen/src/transpile_bindgen.rs
@@ -22,8 +22,9 @@ use wasmtime_environ::{
         GlobalInitializer, InstantiateModule, LoweredIndex, RuntimeImportIndex,
         RuntimeInstanceIndex, StaticModuleIndex, Trampoline, TrampolineIndex,
     },
+    fact::{FixedEncoding, Transcode},
+    EntityIndex, PrimaryMap,
 };
-use wasmtime_environ::{EntityIndex, PrimaryMap};
 use wit_bindgen_core::abi::{self, LiftLower};
 use wit_component::StringEncoding;
 use wit_parser::abi::AbiVariant;
@@ -431,6 +432,7 @@ impl<'a> Instantiator<'a, '_> {
     }
 
     fn trampoline(&mut self, i: TrampolineIndex, trampoline: &'a Trampoline) {
+        let i = i.as_u32();
         match trampoline {
             // these are hoisted before initialization
             Trampoline::LowerImport { .. } => {}
@@ -446,15 +448,48 @@ impl<'a> Instantiator<'a, '_> {
             // for now since it can't be tested and additionally JS doesn't
             // support multi-memory which transcoders rely on anyway.
             Trampoline::Transcoder {
-                op: _,
-                from: _,
-                from64: _,
-                to: _,
-                to64: _,
-            } => unimplemented!(),
+                op,
+                from,
+                from64,
+                to,
+                to64,
+            } => {
+                if *from64 || *to64 {
+                    unimplemented!("memory 64 transcoder");
+                }
+                let from = from.as_u32();
+                let to = to.as_u32();
+                match op {
+                    Transcode::Copy(FixedEncoding::Utf8) => {
+                        uwriteln!(
+                            self.src.js,
+                            "function trampoline{i} (from_ptr, len, to_ptr) {{
+                                new Uint8Array(memory{to}.buffer, to_ptr, len).set(new Uint8Array(memory{from}.buffer, from_ptr, len));
+                            }}
+                            "
+                        );
+                    }
+                    Transcode::Copy(FixedEncoding::Utf16) => unimplemented!("utf16 copier"),
+                    Transcode::Copy(FixedEncoding::Latin1) => unimplemented!("latin1 copier"),
+                    Transcode::Latin1ToUtf16 => unimplemented!("latin to utf16 transcoder"),
+                    Transcode::Latin1ToUtf8 => unimplemented!("latin to utf8 transcoder"),
+                    Transcode::Utf16ToCompactProbablyUtf16 => {
+                        unimplemented!("utf16 to compact wtf16 transcoder")
+                    }
+                    Transcode::Utf16ToCompactUtf16 => {
+                        unimplemented!("utf16 to compact utf16 transcoder")
+                    }
+                    Transcode::Utf16ToLatin1 => unimplemented!("utf16 to latin1 transcoder"),
+                    Transcode::Utf16ToUtf8 => unimplemented!("utf16 to utf8 transcoder"),
+                    Transcode::Utf8ToCompactUtf16 => {
+                        unimplemented!("utf8 to compact utf16 transcoder")
+                    }
+                    Transcode::Utf8ToLatin1 => unimplemented!("utf8 to latin1 transcoder"),
+                    Transcode::Utf8ToUtf16 => unimplemented!("utf8 to utf16 transcoder"),
+                };
+            }
 
             Trampoline::ResourceNew(resource) => {
-                let i = i.as_u32();
                 self.ensure_resource_table(*resource);
                 let rid = resource.as_u32();
                 uwrite!(
@@ -468,7 +503,6 @@ impl<'a> Instantiator<'a, '_> {
                 );
             }
             Trampoline::ResourceRep(resource) => {
-                let i = i.as_u32();
                 self.ensure_resource_table(*resource);
                 let rid = resource.as_u32();
                 uwrite!(
@@ -484,7 +518,6 @@ impl<'a> Instantiator<'a, '_> {
                 );
             }
             Trampoline::ResourceDrop(resource) => {
-                let i = i.as_u32();
                 self.ensure_resource_table(*resource);
                 let rid = resource.as_u32();
                 let resource = &self.types[*resource];
@@ -585,6 +618,7 @@ impl<'a> Instantiator<'a, '_> {
                 prev.is_none(),
                 "unsupported duplicate import of `{module}::{name}`"
             );
+            assert!(prev.is_none());
         }
         let mut imports = String::new();
         if !import_obj.is_empty() {
diff --git a/test/cli.js b/test/cli.js
index 6ada12659..c98455338 100644
--- a/test/cli.js
+++ b/test/cli.js
@@ -1,5 +1,5 @@
 import { deepStrictEqual, ok, strictEqual } from 'node:assert';
-import { readFile, rm } from 'node:fs/promises';
+import { readFile, rm, writeFile } from 'node:fs/promises';
 import { fileURLToPath } from 'url';
 import { exec, jcoPath } from './helpers.js';
 import { tmpdir } from 'node:os';
@@ -18,6 +18,16 @@ export async function cliTest (fixtures) {
       catch {}
     }
 
+    test('Transcoding', async () => {
+      const outDir = fileURLToPath(new URL(`./output/env-allow`, import.meta.url));
+      const { stderr } = await exec(jcoPath, 'transpile', `test/fixtures/env-allow.composed.wasm`, '-o', outDir);
+      strictEqual(stderr, '');
+      await writeFile(`${outDir}/package.json`, JSON.stringify({ type: 'module' }));
+      const source = await readFile(`${outDir}/env-allow.composed.js`);
+      const m = await import(`${outDir}/env-allow.composed.js`);
+      deepStrictEqual(m.testGetEnv(), [['CUSTOM', 'VAL']]);
+    });
+
     test('Transpile', async () => {
       try {
         const name = 'flavorful';
diff --git a/test/fixtures/env-allow.composed.wasm b/test/fixtures/env-allow.composed.wasm
new file mode 100644
index 000000000..37e9cb60b
Binary files /dev/null and b/test/fixtures/env-allow.composed.wasm differ
diff --git a/test/fixtures/virt.wasm b/test/fixtures/virt.wasm
new file mode 100644
index 000000000..1a282c1aa
Binary files /dev/null and b/test/fixtures/virt.wasm differ
diff --git a/update-tests.sh b/update-tests.sh
index c8812a846..b80261445 100755
--- a/update-tests.sh
+++ b/update-tests.sh
@@ -26,3 +26,9 @@ cd ..
 ./src/jco.js componentize test/fixtures/component-gen/import-fn.js --wit test/fixtures/component-gen/import-fn.wit -o test/fixtures/components/import-fn.component.wasm
 
 rm -rf wit-bindgen
+
+## wasi virt to generate composition case
+git clone https://github.com/bytecodealliance/wasi-virt
+cd wasi-virt
+cargo test
+cp tests/generated/env-allow.composed.wasm ../test/fixtures/