diff --git a/cli/Cargo.toml b/cli/Cargo.toml
index 5ee0bd22da..c1779c1022 100644
--- a/cli/Cargo.toml
+++ b/cli/Cargo.toml
@@ -26,6 +26,11 @@ name = "lsp_bench_standalone"
 harness = false
 path = "./bench/lsp_bench_standalone.rs"
 
+[features]
+# A dev feature to disable creations and loading of snapshots in favor of
+# loading JS sources at runtime.
+__runtime_js_sources = ["deno_runtime/__runtime_js_sources"]
+
 [build-dependencies]
 deno_runtime = { workspace = true, features = ["snapshot_from_snapshot", "include_js_files_for_snapshotting"] }
 deno_core = { workspace = true, features = ["include_js_files_for_snapshotting"] }
diff --git a/cli/build.rs b/cli/build.rs
index ecf0d3cbea..206c80d1e8 100644
--- a/cli/build.rs
+++ b/cli/build.rs
@@ -2,16 +2,10 @@
 
 use std::env;
 use std::path::PathBuf;
-use std::sync::Arc;
 
 use deno_core::snapshot_util::*;
-use deno_core::Extension;
 use deno_core::ExtensionFileSource;
 use deno_core::ExtensionFileSourceCode;
-use deno_runtime::deno_cache::SqliteBackedCache;
-use deno_runtime::deno_http::DefaultHttpPropertyExtractor;
-use deno_runtime::deno_kv::sqlite::SqliteDbHandler;
-use deno_runtime::permissions::PermissionsContainer;
 use deno_runtime::*;
 
 mod ts {
@@ -304,12 +298,10 @@ mod ts {
   }
 }
 
-// FIXME(bartlomieju): information about which extensions were
-// already snapshotted is not preserved in the snapshot. This should be
-// fixed, so we can reliably depend on that information.
-// deps = [runtime]
+// Duplicated in `ops/mod.rs`. Keep in sync!
 deno_core::extension!(
   cli,
+  deps = [runtime],
   esm_entry_point = "ext:cli/99_main.js",
   esm = [
     dir "js",
@@ -326,8 +318,16 @@ deno_core::extension!(
   }
 );
 
+#[cfg(not(feature = "__runtime_js_sources"))]
 #[must_use = "The files listed by create_cli_snapshot should be printed as 'cargo:rerun-if-changed' lines"]
 fn create_cli_snapshot(snapshot_path: PathBuf) -> CreateSnapshotOutput {
+  use deno_core::Extension;
+  use deno_runtime::deno_cache::SqliteBackedCache;
+  use deno_runtime::deno_http::DefaultHttpPropertyExtractor;
+  use deno_runtime::deno_kv::sqlite::SqliteDbHandler;
+  use deno_runtime::permissions::PermissionsContainer;
+  use std::sync::Arc;
+
   // NOTE(bartlomieju): ordering is important here, keep it in sync with
   // `runtime/worker.rs`, `runtime/web_worker.rs` and `runtime/build.rs`!
   let fs = Arc::new(deno_fs::RealFs);
@@ -367,13 +367,14 @@ fn create_cli_snapshot(snapshot_path: PathBuf) -> CreateSnapshotOutput {
     deno_io::deno_io::init_ops(Default::default()),
     deno_fs::deno_fs::init_ops::<PermissionsContainer>(false, fs.clone()),
     deno_node::deno_node::init_ops::<PermissionsContainer>(None, fs),
+    deno_runtime::runtime::init_ops(),
     cli::init_ops_and_esm(), // NOTE: This needs to be init_ops_and_esm!
   ];
 
   create_snapshot(CreateSnapshotOptions {
     cargo_manifest_dir: env!("CARGO_MANIFEST_DIR"),
     snapshot_path,
-    startup_snapshot: Some(deno_runtime::js::deno_isolate_init()),
+    startup_snapshot: deno_runtime::js::deno_isolate_init(),
     extensions,
     compression_cb: None,
     with_runtime_cb: None,
@@ -483,10 +484,13 @@ fn main() {
   let compiler_snapshot_path = o.join("COMPILER_SNAPSHOT.bin");
   ts::create_compiler_snapshot(compiler_snapshot_path, &c);
 
-  let cli_snapshot_path = o.join("CLI_SNAPSHOT.bin");
-  let output = create_cli_snapshot(cli_snapshot_path);
-  for path in output.files_loaded_during_snapshot {
-    println!("cargo:rerun-if-changed={}", path.display())
+  #[cfg(not(feature = "__runtime_js_sources"))]
+  {
+    let cli_snapshot_path = o.join("CLI_SNAPSHOT.bin");
+    let output = create_cli_snapshot(cli_snapshot_path);
+    for path in output.files_loaded_during_snapshot {
+      println!("cargo:rerun-if-changed={}", path.display())
+    }
   }
 
   #[cfg(target_os = "windows")]
diff --git a/cli/js.rs b/cli/js.rs
index 6a312a2066..f87bf6d732 100644
--- a/cli/js.rs
+++ b/cli/js.rs
@@ -3,12 +3,20 @@
 use deno_core::Snapshot;
 use log::debug;
 
+#[cfg(not(feature = "__runtime_js_sources"))]
 static CLI_SNAPSHOT: &[u8] =
   include_bytes!(concat!(env!("OUT_DIR"), "/CLI_SNAPSHOT.bin"));
 
-pub fn deno_isolate_init() -> Snapshot {
+pub fn deno_isolate_init() -> Option<Snapshot> {
   debug!("Deno isolate init with snapshots.");
-  Snapshot::Static(CLI_SNAPSHOT)
+  #[cfg(not(feature = "__runtime_js_sources"))]
+  {
+    Some(Snapshot::Static(CLI_SNAPSHOT))
+  }
+  #[cfg(feature = "__runtime_js_sources")]
+  {
+    None
+  }
 }
 
 #[cfg(test)]
@@ -18,7 +26,7 @@ mod tests {
   #[test]
   fn runtime_snapshot() {
     let mut js_runtime = deno_core::JsRuntime::new(deno_core::RuntimeOptions {
-      startup_snapshot: Some(deno_isolate_init()),
+      startup_snapshot: deno_isolate_init(),
       ..Default::default()
     });
     js_runtime
diff --git a/cli/ops/mod.rs b/cli/ops/mod.rs
index 5066c44b9f..7af5f14af5 100644
--- a/cli/ops/mod.rs
+++ b/cli/ops/mod.rs
@@ -12,17 +12,38 @@ pub mod bench;
 pub mod testing;
 
 pub fn cli_exts(npm_resolver: Arc<CliNpmResolver>) -> Vec<Extension> {
-  vec![deno_cli::init_ops(npm_resolver)]
+  vec![
+    #[cfg(not(feature = "__runtime_js_sources"))]
+    cli::init_ops(npm_resolver),
+    #[cfg(feature = "__runtime_js_sources")]
+    cli::init_ops_and_esm(npm_resolver),
+  ]
 }
 
-deno_core::extension!(deno_cli,
+// ESM parts duplicated in `../build.rs`. Keep in sync!
+deno_core::extension!(cli,
+  deps = [runtime],
   ops = [op_npm_process_state],
+  esm_entry_point = "ext:cli/99_main.js",
+  esm = [
+    dir "js",
+    "40_testing.js",
+    "99_main.js"
+  ],
   options = {
     npm_resolver: Arc<CliNpmResolver>,
   },
   state = |state, options| {
     state.put(options.npm_resolver);
   },
+  customizer = |ext: &mut deno_core::Extension| {
+    ext.esm_files.to_mut().push(deno_core::ExtensionFileSource {
+      specifier: "ext:cli/runtime/js/99_main.js",
+      code: deno_core::ExtensionFileSourceCode::LoadedFromFsDuringSnapshot(
+        deno_runtime::js::PATH_FOR_99_MAIN_JS,
+      ),
+    });
+  },
 );
 
 #[op]
diff --git a/cli/worker.rs b/cli/worker.rs
index 235e9a225c..a712dc9c64 100644
--- a/cli/worker.rs
+++ b/cli/worker.rs
@@ -450,7 +450,7 @@ impl CliMainWorkerFactory {
         inspect: shared.options.is_inspecting,
       },
       extensions,
-      startup_snapshot: Some(crate::js::deno_isolate_init()),
+      startup_snapshot: crate::js::deno_isolate_init(),
       create_params: None,
       unsafely_ignore_certificate_errors: shared
         .options
@@ -638,7 +638,7 @@ fn create_web_worker_callback(
         inspect: shared.options.is_inspecting,
       },
       extensions,
-      startup_snapshot: Some(crate::js::deno_isolate_init()),
+      startup_snapshot: crate::js::deno_isolate_init(),
       unsafely_ignore_certificate_errors: shared
         .options
         .unsafely_ignore_certificate_errors
@@ -688,7 +688,7 @@ mod tests {
     let permissions = PermissionsContainer::new(Permissions::default());
 
     let options = WorkerOptions {
-      startup_snapshot: Some(crate::js::deno_isolate_init()),
+      startup_snapshot: crate::js::deno_isolate_init(),
       ..Default::default()
     };
 
diff --git a/ext/node/build.rs b/ext/node/build.rs
new file mode 100644
index 0000000000..778f2da17b
--- /dev/null
+++ b/ext/node/build.rs
@@ -0,0 +1,7 @@
+// Copyright 2018-2023 the Deno authors. All rights reserved. MIT license.
+
+use std::env;
+
+fn main() {
+  println!("cargo:rustc-env=TARGET={}", env::var("TARGET").unwrap());
+}
diff --git a/ext/node/lib.rs b/ext/node/lib.rs
index 40330dc5b0..e2643a84fa 100644
--- a/ext/node/lib.rs
+++ b/ext/node/lib.rs
@@ -132,12 +132,7 @@ pub static NODE_ENV_VAR_ALLOWLIST: Lazy<HashSet<String>> = Lazy::new(|| {
 
 #[op]
 fn op_node_build_os() -> String {
-  std::env::var("TARGET")
-    .unwrap()
-    .split('-')
-    .nth(2)
-    .unwrap()
-    .to_string()
+  env!("TARGET").split('-').nth(2).unwrap().to_string()
 }
 
 #[op(fast)]
diff --git a/runtime/Cargo.toml b/runtime/Cargo.toml
index 4850a52559..a7463920a2 100644
--- a/runtime/Cargo.toml
+++ b/runtime/Cargo.toml
@@ -23,6 +23,9 @@ snapshot_from_snapshot = []
 include_js_files_for_snapshotting = [
   "deno_core/include_js_files_for_snapshotting",
 ]
+# A dev feature to disable creations and loading of snapshots in favor of
+# loading JS sources at runtime.
+__runtime_js_sources = ["dont_create_runtime_snapshot"]
 
 [lib]
 name = "deno_runtime"
@@ -64,6 +67,7 @@ winres.workspace = true
 winapi.workspace = true
 
 [dependencies]
+deno_ast.workspace = true
 deno_broadcast_channel.workspace = true
 deno_cache.workspace = true
 deno_console.workspace = true
diff --git a/runtime/build.rs b/runtime/build.rs
index 64ef246dc8..56f9d611ac 100644
--- a/runtime/build.rs
+++ b/runtime/build.rs
@@ -21,6 +21,7 @@ mod startup_snapshot {
   use deno_http::DefaultHttpPropertyExtractor;
   use std::path::Path;
 
+  // Duplicated in `worker.rs`. Keep in sync!
   fn maybe_transpile_source(
     source: &mut ExtensionFileSource,
   ) -> Result<(), AnyError> {
@@ -240,6 +241,7 @@ mod startup_snapshot {
     }
   }
 
+  // Duplicated in `worker.rs`. Keep in sync!
   deno_core::extension!(runtime,
     deps = [
       deno_webidl,
diff --git a/runtime/js.rs b/runtime/js.rs
index def2724ce3..f942493a3a 100644
--- a/runtime/js.rs
+++ b/runtime/js.rs
@@ -1,17 +1,21 @@
 // Copyright 2018-2023 the Deno authors. All rights reserved. MIT license.
-#[cfg(not(feature = "dont_create_runtime_snapshot"))]
 use deno_core::Snapshot;
-#[cfg(not(feature = "dont_create_runtime_snapshot"))]
 use log::debug;
 
 #[cfg(not(feature = "dont_create_runtime_snapshot"))]
 static RUNTIME_SNAPSHOT: &[u8] =
   include_bytes!(concat!(env!("OUT_DIR"), "/RUNTIME_SNAPSHOT.bin"));
 
-#[cfg(not(feature = "dont_create_runtime_snapshot"))]
-pub fn deno_isolate_init() -> Snapshot {
+pub fn deno_isolate_init() -> Option<Snapshot> {
   debug!("Deno isolate init with snapshots.");
-  Snapshot::Static(RUNTIME_SNAPSHOT)
+  #[cfg(not(feature = "dont_create_runtime_snapshot"))]
+  {
+    Some(Snapshot::Static(RUNTIME_SNAPSHOT))
+  }
+  #[cfg(feature = "dont_create_runtime_snapshot")]
+  {
+    None
+  }
 }
 
 #[cfg(not(feature = "include_js_files_for_snapshotting"))]
diff --git a/runtime/lib.rs b/runtime/lib.rs
index 1e307f492a..248ef94dea 100644
--- a/runtime/lib.rs
+++ b/runtime/lib.rs
@@ -34,5 +34,6 @@ pub mod web_worker;
 pub mod worker;
 
 mod worker_bootstrap;
+pub use worker::runtime;
 pub use worker_bootstrap::BootstrapOptions;
 pub use worker_bootstrap::WorkerLogLevel;
diff --git a/runtime/web_worker.rs b/runtime/web_worker.rs
index af1ae19e0e..a3b93836c3 100644
--- a/runtime/web_worker.rs
+++ b/runtime/web_worker.rs
@@ -4,6 +4,7 @@ use crate::inspector_server::InspectorServer;
 use crate::ops;
 use crate::permissions::PermissionsContainer;
 use crate::tokio_util::create_and_run_current_thread;
+use crate::worker::runtime;
 use crate::worker::FormatJsErrorFn;
 use crate::BootstrapOptions;
 use deno_broadcast_channel::InMemoryBroadcastChannel;
@@ -397,16 +398,17 @@ impl WebWorker {
 
     // NOTE(bartlomieju): ordering is important here, keep it in sync with
     // `runtime/build.rs`, `runtime/worker.rs` and `cli/build.rs`!
-    let mut extensions: Vec<Extension> = vec![
+
+    let mut extensions = vec![
       // Web APIs
-      deno_webidl::deno_webidl::init_ops(),
-      deno_console::deno_console::init_ops(),
-      deno_url::deno_url::init_ops(),
-      deno_web::deno_web::init_ops::<PermissionsContainer>(
+      deno_webidl::deno_webidl::init_ops_and_esm(),
+      deno_console::deno_console::init_ops_and_esm(),
+      deno_url::deno_url::init_ops_and_esm(),
+      deno_web::deno_web::init_ops_and_esm::<PermissionsContainer>(
         options.blob_store.clone(),
         Some(main_module.clone()),
       ),
-      deno_fetch::deno_fetch::init_ops::<PermissionsContainer>(
+      deno_fetch::deno_fetch::init_ops_and_esm::<PermissionsContainer>(
         deno_fetch::Options {
           user_agent: options.bootstrap.user_agent.clone(),
           root_cert_store_provider: options.root_cert_store_provider.clone(),
@@ -417,73 +419,89 @@ impl WebWorker {
           ..Default::default()
         },
       ),
-      deno_cache::deno_cache::init_ops::<SqliteBackedCache>(create_cache),
-      deno_websocket::deno_websocket::init_ops::<PermissionsContainer>(
+      deno_cache::deno_cache::init_ops_and_esm::<SqliteBackedCache>(
+        create_cache,
+      ),
+      deno_websocket::deno_websocket::init_ops_and_esm::<PermissionsContainer>(
         options.bootstrap.user_agent.clone(),
         options.root_cert_store_provider.clone(),
         options.unsafely_ignore_certificate_errors.clone(),
       ),
-      deno_webstorage::deno_webstorage::init_ops(None).disable(),
-      deno_crypto::deno_crypto::init_ops(options.seed),
-      deno_broadcast_channel::deno_broadcast_channel::init_ops(
+      deno_webstorage::deno_webstorage::init_ops_and_esm(None).disable(),
+      deno_crypto::deno_crypto::init_ops_and_esm(options.seed),
+      deno_broadcast_channel::deno_broadcast_channel::init_ops_and_esm(
         options.broadcast_channel.clone(),
         unstable,
       ),
-      deno_ffi::deno_ffi::init_ops::<PermissionsContainer>(unstable),
-      deno_net::deno_net::init_ops::<PermissionsContainer>(
+      deno_ffi::deno_ffi::init_ops_and_esm::<PermissionsContainer>(unstable),
+      deno_net::deno_net::init_ops_and_esm::<PermissionsContainer>(
         options.root_cert_store_provider.clone(),
         unstable,
         options.unsafely_ignore_certificate_errors.clone(),
       ),
-      deno_tls::deno_tls::init_ops(),
-      deno_kv::deno_kv::init_ops(
+      deno_tls::deno_tls::init_ops_and_esm(),
+      deno_kv::deno_kv::init_ops_and_esm(
         SqliteDbHandler::<PermissionsContainer>::new(None),
         unstable,
       ),
-      deno_napi::deno_napi::init_ops::<PermissionsContainer>(),
-      deno_http::deno_http::init_ops::<DefaultHttpPropertyExtractor>(),
-      deno_io::deno_io::init_ops(Some(options.stdio)),
-      deno_fs::deno_fs::init_ops::<PermissionsContainer>(
+      deno_napi::deno_napi::init_ops_and_esm::<PermissionsContainer>(),
+      deno_http::deno_http::init_ops_and_esm::<DefaultHttpPropertyExtractor>(),
+      deno_io::deno_io::init_ops_and_esm(Some(options.stdio)),
+      deno_fs::deno_fs::init_ops_and_esm::<PermissionsContainer>(
         unstable,
         options.fs.clone(),
       ),
-      deno_node::deno_node::init_ops::<PermissionsContainer>(
+      deno_node::deno_node::init_ops_and_esm::<PermissionsContainer>(
         options.npm_resolver,
         options.fs,
       ),
       // Runtime ops that are always initialized for WebWorkers
-      ops::web_worker::deno_web_worker::init_ops(),
-      ops::runtime::deno_runtime::init_ops(main_module.clone()),
-      ops::worker_host::deno_worker_host::init_ops(
+      ops::web_worker::deno_web_worker::init_ops_and_esm(),
+      ops::runtime::deno_runtime::init_ops_and_esm(main_module.clone()),
+      ops::worker_host::deno_worker_host::init_ops_and_esm(
         options.create_web_worker_cb.clone(),
         options.preload_module_cb.clone(),
         options.pre_execute_module_cb.clone(),
         options.format_js_error_fn.clone(),
       ),
-      ops::fs_events::deno_fs_events::init_ops(),
-      ops::os::deno_os_worker::init_ops(),
-      ops::permissions::deno_permissions::init_ops(),
-      ops::process::deno_process::init_ops(),
-      ops::signal::deno_signal::init_ops(),
-      ops::tty::deno_tty::init_ops(),
-      ops::http::deno_http_runtime::init_ops(),
-      deno_permissions_web_worker::init_ops(
+      ops::fs_events::deno_fs_events::init_ops_and_esm(),
+      ops::os::deno_os_worker::init_ops_and_esm(),
+      ops::permissions::deno_permissions::init_ops_and_esm(),
+      ops::process::deno_process::init_ops_and_esm(),
+      ops::signal::deno_signal::init_ops_and_esm(),
+      ops::tty::deno_tty::init_ops_and_esm(),
+      ops::http::deno_http_runtime::init_ops_and_esm(),
+      deno_permissions_web_worker::init_ops_and_esm(
         permissions,
         unstable,
         enable_testing_features,
       ),
+      runtime::init_ops_and_esm(),
     ];
 
-    // Append exts
+    for extension in &mut extensions {
+      #[cfg(not(feature = "__runtime_js_sources"))]
+      {
+        extension.js_files = std::borrow::Cow::Borrowed(&[]);
+        extension.esm_files = std::borrow::Cow::Borrowed(&[]);
+        extension.esm_entry_point = None;
+      }
+      #[cfg(feature = "__runtime_js_sources")]
+      {
+        use crate::worker::maybe_transpile_source;
+        for source in extension.esm_files.to_mut() {
+          maybe_transpile_source(source).unwrap();
+        }
+        for source in extension.js_files.to_mut() {
+          maybe_transpile_source(source).unwrap();
+        }
+      }
+    }
+
     extensions.extend(std::mem::take(&mut options.extensions));
 
-    #[cfg(not(feature = "dont_create_runtime_snapshot"))]
-    let startup_snapshot = options
-      .startup_snapshot
-      .unwrap_or_else(crate::js::deno_isolate_init);
-    #[cfg(feature = "dont_create_runtime_snapshot")]
-    let startup_snapshot = options.startup_snapshot
-      .expect("deno_runtime startup snapshot is not available with 'create_runtime_snapshot' Cargo feature.");
+    #[cfg(all(feature = "include_js_files_for_snapshotting", feature = "dont_create_runtime_snapshot", not(feature = "__runtime_js_sources")))]
+    options.startup_snapshot.as_ref().expect("Sources are not embedded, snapshotting was disabled and a user snapshot was not provided.");
 
     // Clear extension modules from the module map, except preserve `node:*`
     // modules as `node:` specifiers.
@@ -492,7 +510,9 @@ impl WebWorker {
 
     let mut js_runtime = JsRuntime::new(RuntimeOptions {
       module_loader: Some(options.module_loader.clone()),
-      startup_snapshot: Some(startup_snapshot),
+      startup_snapshot: options
+        .startup_snapshot
+        .or_else(crate::js::deno_isolate_init),
       source_map_getter: options.source_map_getter,
       get_error_class_fn: options.get_error_class_fn,
       shared_array_buffer_store: options.shared_array_buffer_store.clone(),
diff --git a/runtime/worker.rs b/runtime/worker.rs
index 5ce75cf718..060f5537bd 100644
--- a/runtime/worker.rs
+++ b/runtime/worker.rs
@@ -18,6 +18,8 @@ use deno_core::futures::Future;
 use deno_core::v8;
 use deno_core::CompiledWasmModuleStore;
 use deno_core::Extension;
+#[cfg(feature = "__runtime_js_sources")]
+use deno_core::ExtensionFileSource;
 use deno_core::FsModuleLoader;
 use deno_core::GetErrorClassFn;
 use deno_core::JsRuntime;
@@ -59,6 +61,78 @@ impl ExitCode {
   }
 }
 
+// Duplicated in `build.rs`. Keep in sync!
+deno_core::extension!(
+  runtime,
+  esm_entry_point = "ext:runtime/90_deno_ns.js",
+  esm = [
+    dir "js",
+    "01_errors.js",
+    "01_version.ts",
+    "06_util.js",
+    "10_permissions.js",
+    "11_workers.js",
+    "13_buffer.js",
+    "30_os.js",
+    "40_fs_events.js",
+    "40_http.js",
+    "40_process.js",
+    "40_signals.js",
+    "40_tty.js",
+    "41_prompt.js",
+    "90_deno_ns.js",
+    "98_global_scope.js"
+  ],
+);
+
+// Duplicated in `build.rs`. Keep in sync!
+#[cfg(feature = "__runtime_js_sources")]
+pub fn maybe_transpile_source(
+  source: &mut ExtensionFileSource,
+) -> Result<(), AnyError> {
+  use deno_ast::MediaType;
+  use deno_ast::ParseParams;
+  use deno_ast::SourceTextInfo;
+  use deno_core::ExtensionFileSourceCode;
+  use std::path::Path;
+
+  // Always transpile `node:` built-in modules, since they might be TypeScript.
+  let media_type = if source.specifier.starts_with("node:") {
+    MediaType::TypeScript
+  } else {
+    MediaType::from_path(Path::new(&source.specifier))
+  };
+
+  match media_type {
+    MediaType::TypeScript => {}
+    MediaType::JavaScript => return Ok(()),
+    MediaType::Mjs => return Ok(()),
+    _ => panic!(
+      "Unsupported media type for snapshotting {media_type:?} for file {}",
+      source.specifier
+    ),
+  }
+  let code = source.load()?;
+
+  let parsed = deno_ast::parse_module(ParseParams {
+    specifier: source.specifier.to_string(),
+    text_info: SourceTextInfo::from_string(code.as_str().to_owned()),
+    media_type,
+    capture_tokens: false,
+    scope_analysis: false,
+    maybe_syntax: None,
+  })?;
+  let transpiled_source = parsed.transpile(&deno_ast::EmitOptions {
+    imports_not_used_as_values: deno_ast::ImportsNotUsedAsValues::Remove,
+    inline_source_map: false,
+    ..Default::default()
+  })?;
+
+  source.code =
+    ExtensionFileSourceCode::Computed(transpiled_source.text.into());
+  Ok(())
+}
+
 /// This worker is created and used by almost all
 /// subcommands in Deno executable.
 ///
@@ -226,14 +300,14 @@ impl MainWorker {
     // `runtime/build.rs`, `runtime/web_worker.rs` and `cli/build.rs`!
     let mut extensions = vec![
       // Web APIs
-      deno_webidl::deno_webidl::init_ops(),
-      deno_console::deno_console::init_ops(),
-      deno_url::deno_url::init_ops(),
-      deno_web::deno_web::init_ops::<PermissionsContainer>(
+      deno_webidl::deno_webidl::init_ops_and_esm(),
+      deno_console::deno_console::init_ops_and_esm(),
+      deno_url::deno_url::init_ops_and_esm(),
+      deno_web::deno_web::init_ops_and_esm::<PermissionsContainer>(
         options.blob_store.clone(),
         options.bootstrap.location.clone(),
       ),
-      deno_fetch::deno_fetch::init_ops::<PermissionsContainer>(
+      deno_fetch::deno_fetch::init_ops_and_esm::<PermissionsContainer>(
         deno_fetch::Options {
           user_agent: options.bootstrap.user_agent.clone(),
           root_cert_store_provider: options.root_cert_store_provider.clone(),
@@ -244,75 +318,91 @@ impl MainWorker {
           ..Default::default()
         },
       ),
-      deno_cache::deno_cache::init_ops::<SqliteBackedCache>(create_cache),
-      deno_websocket::deno_websocket::init_ops::<PermissionsContainer>(
+      deno_cache::deno_cache::init_ops_and_esm::<SqliteBackedCache>(
+        create_cache,
+      ),
+      deno_websocket::deno_websocket::init_ops_and_esm::<PermissionsContainer>(
         options.bootstrap.user_agent.clone(),
         options.root_cert_store_provider.clone(),
         options.unsafely_ignore_certificate_errors.clone(),
       ),
-      deno_webstorage::deno_webstorage::init_ops(
+      deno_webstorage::deno_webstorage::init_ops_and_esm(
         options.origin_storage_dir.clone(),
       ),
-      deno_crypto::deno_crypto::init_ops(options.seed),
-      deno_broadcast_channel::deno_broadcast_channel::init_ops(
+      deno_crypto::deno_crypto::init_ops_and_esm(options.seed),
+      deno_broadcast_channel::deno_broadcast_channel::init_ops_and_esm(
         options.broadcast_channel.clone(),
         unstable,
       ),
-      deno_ffi::deno_ffi::init_ops::<PermissionsContainer>(unstable),
-      deno_net::deno_net::init_ops::<PermissionsContainer>(
+      deno_ffi::deno_ffi::init_ops_and_esm::<PermissionsContainer>(unstable),
+      deno_net::deno_net::init_ops_and_esm::<PermissionsContainer>(
         options.root_cert_store_provider.clone(),
         unstable,
         options.unsafely_ignore_certificate_errors.clone(),
       ),
-      deno_tls::deno_tls::init_ops(),
-      deno_kv::deno_kv::init_ops(
+      deno_tls::deno_tls::init_ops_and_esm(),
+      deno_kv::deno_kv::init_ops_and_esm(
         SqliteDbHandler::<PermissionsContainer>::new(
           options.origin_storage_dir.clone(),
         ),
         unstable,
       ),
-      deno_napi::deno_napi::init_ops::<PermissionsContainer>(),
-      deno_http::deno_http::init_ops::<DefaultHttpPropertyExtractor>(),
-      deno_io::deno_io::init_ops(Some(options.stdio)),
-      deno_fs::deno_fs::init_ops::<PermissionsContainer>(
+      deno_napi::deno_napi::init_ops_and_esm::<PermissionsContainer>(),
+      deno_http::deno_http::init_ops_and_esm::<DefaultHttpPropertyExtractor>(),
+      deno_io::deno_io::init_ops_and_esm(Some(options.stdio)),
+      deno_fs::deno_fs::init_ops_and_esm::<PermissionsContainer>(
         unstable,
         options.fs.clone(),
       ),
-      deno_node::deno_node::init_ops::<PermissionsContainer>(
+      deno_node::deno_node::init_ops_and_esm::<PermissionsContainer>(
         options.npm_resolver,
         options.fs,
       ),
       // Ops from this crate
-      ops::runtime::deno_runtime::init_ops(main_module.clone()),
-      ops::worker_host::deno_worker_host::init_ops(
+      ops::runtime::deno_runtime::init_ops_and_esm(main_module.clone()),
+      ops::worker_host::deno_worker_host::init_ops_and_esm(
         options.create_web_worker_cb.clone(),
         options.web_worker_preload_module_cb.clone(),
         options.web_worker_pre_execute_module_cb.clone(),
         options.format_js_error_fn.clone(),
       ),
-      ops::fs_events::deno_fs_events::init_ops(),
-      ops::os::deno_os::init_ops(exit_code.clone()),
-      ops::permissions::deno_permissions::init_ops(),
-      ops::process::deno_process::init_ops(),
-      ops::signal::deno_signal::init_ops(),
-      ops::tty::deno_tty::init_ops(),
-      ops::http::deno_http_runtime::init_ops(),
-      deno_permissions_worker::init_ops(
+      ops::fs_events::deno_fs_events::init_ops_and_esm(),
+      ops::os::deno_os::init_ops_and_esm(exit_code.clone()),
+      ops::permissions::deno_permissions::init_ops_and_esm(),
+      ops::process::deno_process::init_ops_and_esm(),
+      ops::signal::deno_signal::init_ops_and_esm(),
+      ops::tty::deno_tty::init_ops_and_esm(),
+      ops::http::deno_http_runtime::init_ops_and_esm(),
+      deno_permissions_worker::init_ops_and_esm(
         permissions,
         unstable,
         enable_testing_features,
       ),
+      runtime::init_ops_and_esm(),
     ];
 
+    for extension in &mut extensions {
+      #[cfg(not(feature = "__runtime_js_sources"))]
+      {
+        extension.js_files = std::borrow::Cow::Borrowed(&[]);
+        extension.esm_files = std::borrow::Cow::Borrowed(&[]);
+        extension.esm_entry_point = None;
+      }
+      #[cfg(feature = "__runtime_js_sources")]
+      {
+        for source in extension.esm_files.to_mut() {
+          maybe_transpile_source(source).unwrap();
+        }
+        for source in extension.js_files.to_mut() {
+          maybe_transpile_source(source).unwrap();
+        }
+      }
+    }
+
     extensions.extend(std::mem::take(&mut options.extensions));
 
-    #[cfg(not(feature = "dont_create_runtime_snapshot"))]
-    let startup_snapshot = options
-      .startup_snapshot
-      .unwrap_or_else(crate::js::deno_isolate_init);
-    #[cfg(feature = "dont_create_runtime_snapshot")]
-    let startup_snapshot = options.startup_snapshot
-      .expect("deno_runtime startup snapshot is not available with 'create_runtime_snapshot' Cargo feature.");
+    #[cfg(all(feature = "include_js_files_for_snapshotting", feature = "dont_create_runtime_snapshot", not(feature = "__runtime_js_sources")))]
+    options.startup_snapshot.as_ref().expect("Sources are not embedded, snapshotting was disabled and a user snapshot was not provided.");
 
     // Clear extension modules from the module map, except preserve `node:*`
     // modules.
@@ -321,7 +411,9 @@ impl MainWorker {
 
     let mut js_runtime = JsRuntime::new(RuntimeOptions {
       module_loader: Some(options.module_loader.clone()),
-      startup_snapshot: Some(startup_snapshot),
+      startup_snapshot: options
+        .startup_snapshot
+        .or_else(crate::js::deno_isolate_init),
       create_params: options.create_params,
       source_map_getter: options.source_map_getter,
       get_error_class_fn: options.get_error_class_fn,