refactor: split worker and worker host logic (#3722)

* split ops/worker.rs into ops/worker_host.rs and ops/web_worker.rs

* refactor js/workers.ts and factor out js/worker_main.ts - entry point for WebWorker runtime

* BREAKING CHANGE: remove support for blob: URL in Worker

* BREAKING CHANGE: remove Deno namespace support and noDenoNamespace option in Worker constructor

* introduce WebWorker struct which is a stripped down version of cli::Worker

20 files changed, 439 insertions, 265 deletions

diff --git a/cli/compilers/ts.rs b/cli/compilers/ts.rs
index e8abbcd27..037043368 100644
--- a/cli/compilers/ts.rs
+++ b/cli/compilers/ts.rs
@@ -231,7 +231,7 @@ impl TsCompiler {
   fn setup_worker(global_state: ThreadSafeGlobalState) -> Worker {
     let (int, ext) = ThreadSafeState::create_channels();
     let worker_state =
-      ThreadSafeState::new(global_state.clone(), None, None, true, int)
+      ThreadSafeState::new(global_state.clone(), None, None, int)
         .expect("Unable to create worker state");
 
     // Count how many times we start the compiler worker.
diff --git a/cli/compilers/wasm.rs b/cli/compilers/wasm.rs
index e3297283b..ca889be1f 100644
--- a/cli/compilers/wasm.rs
+++ b/cli/compilers/wasm.rs
@@ -45,7 +45,7 @@ impl WasmCompiler {
   fn setup_worker(global_state: ThreadSafeGlobalState) -> Worker {
     let (int, ext) = ThreadSafeState::create_channels();
     let worker_state =
-      ThreadSafeState::new(global_state.clone(), None, None, true, int)
+      ThreadSafeState::new(global_state.clone(), None, None, int)
         .expect("Unable to create worker state");
 
     // Count how many times we start the compiler worker.
diff --git a/cli/js/compiler.ts b/cli/js/compiler.ts
index 79b9fdaf6..7addfc5ca 100644
--- a/cli/js/compiler.ts
+++ b/cli/js/compiler.ts
@@ -32,7 +32,7 @@ import { fromTypeScriptDiagnostic } from "./diagnostics_util.ts";
 import * as os from "./os.ts";
 import { assert } from "./util.ts";
 import * as util from "./util.ts";
-import { postMessage, workerClose, workerMain } from "./workers.ts";
+import { postMessage, workerClose, workerMain } from "./worker_main.ts";
 
 const self = globalThis;
 
diff --git a/cli/js/globals.ts b/cli/js/globals.ts
index 5754002c0..0f364b8e0 100644
--- a/cli/js/globals.ts
+++ b/cli/js/globals.ts
@@ -21,6 +21,7 @@ import * as textEncoding from "./text_encoding.ts";
 import * as timers from "./timers.ts";
 import * as url from "./url.ts";
 import * as urlSearchParams from "./url_search_params.ts";
+import * as workerRuntime from "./worker_main.ts";
 import * as workers from "./workers.ts";
 import * as performanceUtil from "./performance.ts";
 import * as request from "./request.ts";
@@ -194,12 +195,12 @@ const globalProperties = {
   Response: nonEnumerable(fetchTypes.Response),
   performance: writable(new performanceUtil.Performance()),
 
-  onmessage: writable(workers.onmessage),
-  onerror: writable(workers.onerror),
+  onmessage: writable(workerRuntime.onmessage),
+  onerror: writable(workerRuntime.onerror),
 
-  workerMain: nonEnumerable(workers.workerMain),
-  workerClose: nonEnumerable(workers.workerClose),
-  postMessage: writable(workers.postMessage),
+  workerMain: nonEnumerable(workerRuntime.workerMain),
+  workerClose: nonEnumerable(workerRuntime.workerClose),
+  postMessage: writable(workerRuntime.postMessage),
   Worker: nonEnumerable(workers.WorkerImpl),
 
   [domTypes.eventTargetHost]: nonEnumerable(null),
diff --git a/cli/js/lib.deno_runtime.d.ts b/cli/js/lib.deno_runtime.d.ts
index 0fa183348..05553ffb7 100644
--- a/cli/js/lib.deno_runtime.d.ts
+++ b/cli/js/lib.deno_runtime.d.ts
@@ -2128,9 +2128,9 @@ declare interface Window {
   performance: __performanceUtil.Performance;
   onmessage: (e: { data: any }) => void;
   onerror: undefined | typeof onerror;
-  workerMain: typeof __workers.workerMain;
-  workerClose: typeof __workers.workerClose;
-  postMessage: typeof __workers.postMessage;
+  workerMain: typeof __workerMain.workerMain;
+  workerClose: typeof __workerMain.workerClose;
+  postMessage: typeof __workerMain.postMessage;
   Worker: typeof __workers.WorkerImpl;
   addEventListener: (
     type: string,
@@ -2187,9 +2187,9 @@ declare let onerror:
       e: Event
     ) => boolean | void)
   | undefined;
-declare const workerMain: typeof __workers.workerMain;
-declare const workerClose: typeof __workers.workerClose;
-declare const postMessage: typeof __workers.postMessage;
+declare const workerMain: typeof __workerMain.workerMain;
+declare const workerClose: typeof __workerMain.workerClose;
+declare const postMessage: typeof __workerMain.postMessage;
 declare const Worker: typeof __workers.WorkerImpl;
 declare const addEventListener: (
   type: string,
@@ -3437,31 +3437,25 @@ declare namespace __url {
   };
 }
 
-declare namespace __workers {
-  // @url js/workers.d.ts
-
-  export function encodeMessage(data: any): Uint8Array;
-  export function decodeMessage(dataIntArray: Uint8Array): any;
+declare namespace __workerMain {
   export let onmessage: (e: { data: any }) => void;
   export function postMessage(data: any): void;
   export function getMessage(): Promise<any>;
   export let isClosing: boolean;
   export function workerClose(): void;
   export function workerMain(): Promise<void>;
+}
+
+declare namespace __workers {
+  // @url js/workers.d.ts
   export interface Worker {
     onerror?: (e: Event) => void;
     onmessage?: (e: { data: any }) => void;
     onmessageerror?: () => void;
     postMessage(data: any): void;
-    closed: Promise<void>;
   }
-  export interface WorkerOptions {}
-  /** Extended Deno Worker initialization options.
-   * `noDenoNamespace` hides global `window.Deno` namespace for
-   * spawned worker and nested workers spawned by it (default: false).
-   */
-  export interface DenoWorkerOptions extends WorkerOptions {
-    noDenoNamespace?: boolean;
+  export interface WorkerOptions {
+    type?: "classic" | "module";
   }
   export class WorkerImpl implements Worker {
     private readonly id;
@@ -3470,8 +3464,7 @@ declare namespace __workers {
     onerror?: (e: Event) => void;
     onmessage?: (data: any) => void;
     onmessageerror?: () => void;
-    constructor(specifier: string, options?: DenoWorkerOptions);
-    readonly closed: Promise<void>;
+    constructor(specifier: string, options?: WorkerOptions);
     postMessage(data: any): void;
     private run;
   }
diff --git a/cli/js/worker_main.ts b/cli/js/worker_main.ts
new file mode 100644
index 000000000..cb70057ea
--- /dev/null
+++ b/cli/js/worker_main.ts
@@ -0,0 +1,98 @@
+// Copyright 2018-2020 the Deno authors. All rights reserved. MIT license.
+/* eslint-disable @typescript-eslint/no-explicit-any */
+import { core } from "./core.ts";
+import * as dispatch from "./dispatch.ts";
+import { sendAsync, sendSync } from "./dispatch_json.ts";
+import { log } from "./util.ts";
+import { TextDecoder, TextEncoder } from "./text_encoding.ts";
+
+const encoder = new TextEncoder();
+const decoder = new TextDecoder();
+
+function encodeMessage(data: any): Uint8Array {
+  const dataJson = JSON.stringify(data);
+  return encoder.encode(dataJson);
+}
+
+function decodeMessage(dataIntArray: Uint8Array): any {
+  const dataJson = decoder.decode(dataIntArray);
+  return JSON.parse(dataJson);
+}
+
+// Stuff for workers
+export const onmessage: (e: { data: any }) => void = (): void => {};
+export const onerror: (e: { data: any }) => void = (): void => {};
+
+export function postMessage(data: any): void {
+  const dataIntArray = encodeMessage(data);
+  sendSync(dispatch.OP_WORKER_POST_MESSAGE, {}, dataIntArray);
+}
+
+export async function getMessage(): Promise<any> {
+  log("getMessage");
+  const res = await sendAsync(dispatch.OP_WORKER_GET_MESSAGE);
+  if (res.data != null) {
+    return decodeMessage(new Uint8Array(res.data));
+  } else {
+    return null;
+  }
+}
+
+export let isClosing = false;
+
+export function workerClose(): void {
+  isClosing = true;
+}
+
+export async function workerMain(): Promise<void> {
+  const ops = core.ops();
+  // TODO(bartlomieju): this is a prototype, we should come up with
+  // something a bit more sophisticated
+  for (const [name, opId] of Object.entries(ops)) {
+    const opName = `OP_${name.toUpperCase()}`;
+    // Assign op ids to actual variables
+    // TODO(ry) This type casting is gross and should be fixed.
+    ((dispatch as unknown) as { [key: string]: number })[opName] = opId;
+    core.setAsyncHandler(opId, dispatch.getAsyncHandler(opName));
+  }
+
+  log("workerMain");
+
+  while (!isClosing) {
+    const data = await getMessage();
+    if (data == null) {
+      log("workerMain got null message. quitting.");
+      break;
+    }
+
+    let result: void | Promise<void>;
+    const event = { data };
+
+    try {
+      if (!globalThis["onmessage"]) {
+        break;
+      }
+      result = globalThis.onmessage!(event);
+      if (result && "then" in result) {
+        await result;
+      }
+      if (!globalThis["onmessage"]) {
+        break;
+      }
+    } catch (e) {
+      if (globalThis["onerror"]) {
+        const result = globalThis.onerror(
+          e.message,
+          e.fileName,
+          e.lineNumber,
+          e.columnNumber,
+          e
+        );
+        if (result === true) {
+          continue;
+        }
+      }
+      throw e;
+    }
+  }
+}
diff --git a/cli/js/workers.ts b/cli/js/workers.ts
index 7e8219e19..60ef73da0 100644
--- a/cli/js/workers.ts
+++ b/cli/js/workers.ts
@@ -2,35 +2,35 @@
 /* eslint-disable @typescript-eslint/no-explicit-any */
 import * as dispatch from "./dispatch.ts";
 import { sendAsync, sendSync } from "./dispatch_json.ts";
-import { log, createResolvable, Resolvable } from "./util.ts";
+import { log } from "./util.ts";
 import { TextDecoder, TextEncoder } from "./text_encoding.ts";
+/*
 import { blobURLMap } from "./url.ts";
 import { blobBytesWeakMap } from "./blob.ts";
+*/
 import { Event } from "./event.ts";
 import { EventTarget } from "./event_target.ts";
 
 const encoder = new TextEncoder();
 const decoder = new TextDecoder();
 
-export function encodeMessage(data: any): Uint8Array {
+function encodeMessage(data: any): Uint8Array {
   const dataJson = JSON.stringify(data);
   return encoder.encode(dataJson);
 }
 
-export function decodeMessage(dataIntArray: Uint8Array): any {
+function decodeMessage(dataIntArray: Uint8Array): any {
   const dataJson = decoder.decode(dataIntArray);
   return JSON.parse(dataJson);
 }
 
 function createWorker(
   specifier: string,
-  includeDenoNamespace: boolean,
   hasSourceCode: boolean,
   sourceCode: Uint8Array
 ): { id: number; loaded: boolean } {
   return sendSync(dispatch.OP_CREATE_WORKER, {
     specifier,
-    includeDenoNamespace,
     hasSourceCode,
     sourceCode: new TextDecoder().decode(sourceCode)
   });
@@ -67,92 +67,15 @@ async function hostGetMessage(id: number): Promise<any> {
   }
 }
 
-// Stuff for workers
-export const onmessage: (e: { data: any }) => void = (): void => {};
-export const onerror: (e: { data: any }) => void = (): void => {};
-
-export function postMessage(data: any): void {
-  const dataIntArray = encodeMessage(data);
-  sendSync(dispatch.OP_WORKER_POST_MESSAGE, {}, dataIntArray);
-}
-
-export async function getMessage(): Promise<any> {
-  log("getMessage");
-  const res = await sendAsync(dispatch.OP_WORKER_GET_MESSAGE);
-  if (res.data != null) {
-    return decodeMessage(new Uint8Array(res.data));
-  } else {
-    return null;
-  }
-}
-
-export let isClosing = false;
-
-export function workerClose(): void {
-  isClosing = true;
-}
-
-export async function workerMain(): Promise<void> {
-  log("workerMain");
-
-  while (!isClosing) {
-    const data = await getMessage();
-    if (data == null) {
-      log("workerMain got null message. quitting.");
-      break;
-    }
-
-    let result: void | Promise<void>;
-    const event = { data };
-
-    try {
-      if (!globalThis["onmessage"]) {
-        break;
-      }
-      result = globalThis.onmessage!(event);
-      if (result && "then" in result) {
-        await result;
-      }
-      if (!globalThis["onmessage"]) {
-        break;
-      }
-    } catch (e) {
-      if (globalThis["onerror"]) {
-        const result = globalThis.onerror(
-          e.message,
-          e.fileName,
-          e.lineNumber,
-          e.columnNumber,
-          e
-        );
-        if (result === true) {
-          continue;
-        }
-      }
-      throw e;
-    }
-  }
-}
-
 export interface Worker {
   onerror?: (e: any) => void;
   onmessage?: (e: { data: any }) => void;
   onmessageerror?: () => void;
   postMessage(data: any): void;
-  // TODO(bartlomieju): remove this
-  closed: Promise<void>;
 }
 
-// TODO(kevinkassimo): Maybe implement reasonable web worker options?
-// eslint-disable-next-line @typescript-eslint/no-empty-interface
-export interface WorkerOptions {}
-
-/** Extended Deno Worker initialization options.
- * `noDenoNamespace` hides global `globalThis.Deno` namespace for
- * spawned worker and nested workers spawned by it (default: false).
- */
-export interface DenoWorkerOptions extends WorkerOptions {
-  noDenoNamespace?: boolean;
+export interface WorkerOptions {
+  type?: "classic" | "module";
 }
 
 export class WorkerImpl extends EventTarget implements Worker {
@@ -160,20 +83,29 @@ export class WorkerImpl extends EventTarget implements Worker {
   private isClosing = false;
   private messageBuffer: any[] = [];
   private ready = false;
-  private readonly isClosedPromise: Resolvable<void>;
   public onerror?: (e: any) => void;
   public onmessage?: (data: any) => void;
   public onmessageerror?: () => void;
 
-  constructor(specifier: string, options?: DenoWorkerOptions) {
+  constructor(specifier: string, options?: WorkerOptions) {
     super();
-    let hasSourceCode = false;
-    let sourceCode = new Uint8Array();
 
-    let includeDenoNamespace = true;
-    if (options && options.noDenoNamespace) {
-      includeDenoNamespace = false;
+    let type = "classic";
+
+    if (options?.type) {
+      type = options.type;
+    }
+
+    if (type !== "module") {
+      throw new Error(
+        'Not yet implemented: only "module" type workers are supported'
+      );
     }
+
+    const hasSourceCode = false;
+    const sourceCode = new Uint8Array();
+
+    /* TODO(bartlomieju):
     // Handle blob URL.
     if (specifier.startsWith("blob:")) {
       hasSourceCode = true;
@@ -187,23 +119,14 @@ export class WorkerImpl extends EventTarget implements Worker {
       }
       sourceCode = blobBytes!;
     }
+    */
 
-    const { id, loaded } = createWorker(
-      specifier,
-      includeDenoNamespace,
-      hasSourceCode,
-      sourceCode
-    );
+    const { id, loaded } = createWorker(specifier, hasSourceCode, sourceCode);
     this.id = id;
     this.ready = loaded;
-    this.isClosedPromise = createResolvable();
     this.poll();
   }
 
-  get closed(): Promise<void> {
-    return this.isClosedPromise;
-  }
-
   private handleError(e: any): boolean {
     // TODO: this is being handled in a type unsafe way, it should be type safe
     // eslint-disable-next-line @typescript-eslint/no-explicit-any
@@ -259,7 +182,6 @@ export class WorkerImpl extends EventTarget implements Worker {
       } else {
         this.isClosing = true;
         hostCloseWorker(this.id);
-        this.isClosedPromise.resolve();
         break;
       }
     }
diff --git a/cli/lib.rs b/cli/lib.rs
index a57f224e2..e9a62375a 100644
--- a/cli/lib.rs
+++ b/cli/lib.rs
@@ -51,6 +51,7 @@ pub mod state;
 pub mod test_util;
 mod tokio_util;
 pub mod version;
+mod web_worker;
 pub mod worker;
 
 use crate::deno_error::js_check;
@@ -120,7 +121,6 @@ fn create_worker_and_state(
     global_state.clone(),
     None,
     global_state.main_module.clone(),
-    true,
     int,
   )
   .map_err(deno_error::print_err_and_exit)
@@ -346,16 +346,15 @@ fn bundle_command(flags: DenoFlags) {
 
 fn run_repl(flags: DenoFlags) {
   let (mut worker, _state) = create_worker_and_state(flags);
-  // Make repl continue to function under uncaught async errors.
-  worker.set_error_handler(Box::new(|err| {
-    eprintln!("{}", err.to_string());
-    Ok(())
-  }));
-  // Setup runtime.
   js_check(worker.execute("denoMain()"));
   let main_future = async move {
-    let result = worker.await;
-    js_check(result);
+    loop {
+      let result = worker.clone().await;
+      if let Err(err) = result {
+        eprintln!("{}", err.to_string());
+        worker.clear_exception();
+      }
+    }
   };
   tokio_util::run(main_future);
 }
diff --git a/cli/ops/mod.rs b/cli/ops/mod.rs
index f93c5a060..203d1e17e 100644
--- a/cli/ops/mod.rs
+++ b/cli/ops/mod.rs
@@ -23,4 +23,5 @@ pub mod repl;
 pub mod resources;
 pub mod timers;
 pub mod tls;
-pub mod workers;
+pub mod web_worker;
+pub mod worker_host;
diff --git a/cli/ops/web_worker.rs b/cli/ops/web_worker.rs
new file mode 100644
index 000000000..300a0dfd1
--- /dev/null
+++ b/cli/ops/web_worker.rs
@@ -0,0 +1,77 @@
+// Copyright 2018-2020 the Deno authors. All rights reserved. MIT license.
+use super::dispatch_json::{JsonOp, Value};
+use crate::deno_error::DenoError;
+use crate::deno_error::ErrorKind;
+use crate::ops::json_op;
+use crate::state::ThreadSafeState;
+use deno_core::*;
+use futures;
+use futures::future::FutureExt;
+use futures::sink::SinkExt;
+use futures::stream::StreamExt;
+use std;
+use std::convert::From;
+use std::future::Future;
+use std::pin::Pin;
+use std::task::Context;
+use std::task::Poll;
+
+pub fn init(i: &mut Isolate, s: &ThreadSafeState) {
+  i.register_op(
+    "worker_post_message",
+    s.core_op(json_op(s.stateful_op(op_worker_post_message))),
+  );
+  i.register_op(
+    "worker_get_message",
+    s.core_op(json_op(s.stateful_op(op_worker_get_message))),
+  );
+}
+
+struct GetMessageFuture {
+  state: ThreadSafeState,
+}
+
+impl Future for GetMessageFuture {
+  type Output = Option<Buf>;
+
+  fn poll(self: Pin<&mut Self>, cx: &mut Context) -> Poll<Self::Output> {
+    let inner = self.get_mut();
+    let mut channels = inner.state.worker_channels.lock().unwrap();
+    let receiver = &mut channels.receiver;
+    receiver.poll_next_unpin(cx)
+  }
+}
+
+/// Get message from host as guest worker
+fn op_worker_get_message(
+  state: &ThreadSafeState,
+  _args: Value,
+  _data: Option<PinnedBuf>,
+) -> Result<JsonOp, ErrBox> {
+  let op = GetMessageFuture {
+    state: state.clone(),
+  };
+
+  let op = async move {
+    let maybe_buf = op.await;
+    debug!("op_worker_get_message");
+    Ok(json!({ "data": maybe_buf }))
+  };
+
+  Ok(JsonOp::Async(op.boxed()))
+}
+
+/// Post message to host as guest worker
+fn op_worker_post_message(
+  state: &ThreadSafeState,
+  _args: Value,
+  data: Option<PinnedBuf>,
+) -> Result<JsonOp, ErrBox> {
+  let d = Vec::from(data.unwrap().as_ref()).into_boxed_slice();
+  let mut channels = state.worker_channels.lock().unwrap();
+  let sender = &mut channels.sender;
+  futures::executor::block_on(sender.send(d))
+    .map_err(|e| DenoError::new(ErrorKind::Other, e.to_string()))?;
+
+  Ok(JsonOp::Sync(json!({})))
+}
diff --git a/cli/ops/workers.rs b/cli/ops/worker_host.rs
index eeffb3930..c17dee444 100644
--- a/cli/ops/workers.rs
+++ b/cli/ops/worker_host.rs
@@ -9,7 +9,7 @@ use crate::fmt_errors::JSError;
 use crate::ops::json_op;
 use crate::startup_data;
 use crate::state::ThreadSafeState;
-use crate::worker::Worker;
+use crate::web_worker::WebWorker;
 use deno_core::*;
 use futures;
 use futures::channel::mpsc;
@@ -54,15 +54,6 @@ pub fn init(i: &mut Isolate, s: &ThreadSafeState) {
     "host_get_message",
     s.core_op(json_op(s.stateful_op(op_host_get_message))),
   );
-  // TODO: make sure these two ops are only accessible to appropriate Worker
-  i.register_op(
-    "worker_post_message",
-    s.core_op(json_op(s.stateful_op(op_worker_post_message))),
-  );
-  i.register_op(
-    "worker_get_message",
-    s.core_op(json_op(s.stateful_op(op_worker_get_message))),
-  );
   i.register_op("metrics", s.core_op(json_op(s.stateful_op(op_metrics))));
 }
 
@@ -81,45 +72,10 @@ impl Future for GetMessageFuture {
   }
 }
 
-/// Get message from host as guest worker
-fn op_worker_get_message(
-  state: &ThreadSafeState,
-  _args: Value,
-  _data: Option<PinnedBuf>,
-) -> Result<JsonOp, ErrBox> {
-  let op = GetMessageFuture {
-    state: state.clone(),
-  };
-
-  let op = async move {
-    let maybe_buf = op.await;
-    debug!("op_worker_get_message");
-    Ok(json!({ "data": maybe_buf }))
-  };
-
-  Ok(JsonOp::Async(op.boxed()))
-}
-
-/// Post message to host as guest worker
-fn op_worker_post_message(
-  state: &ThreadSafeState,
-  _args: Value,
-  data: Option<PinnedBuf>,
-) -> Result<JsonOp, ErrBox> {
-  let d = Vec::from(data.unwrap().as_ref()).into_boxed_slice();
-  let mut channels = state.worker_channels.lock().unwrap();
-  let sender = &mut channels.sender;
-  futures::executor::block_on(sender.send(d))
-    .map_err(|e| DenoError::new(ErrorKind::Other, e.to_string()))?;
-
-  Ok(JsonOp::Sync(json!({})))
-}
-
 #[derive(Deserialize)]
 #[serde(rename_all = "camelCase")]
 struct CreateWorkerArgs {
   specifier: String,
-  include_deno_namespace: bool,
   has_source_code: bool,
   source_code: String,
 }
@@ -133,10 +89,6 @@ fn op_create_worker(
   let args: CreateWorkerArgs = serde_json::from_value(args)?;
 
   let specifier = args.specifier.as_ref();
-  // Only include deno namespace if requested AND current worker
-  // has included namespace (to avoid escalation).
-  let include_deno_namespace =
-    args.include_deno_namespace && state.include_deno_namespace;
   let has_source_code = args.has_source_code;
   let source_code = args.source_code;
 
@@ -156,16 +108,13 @@ fn op_create_worker(
     state.global_state.clone(),
     Some(parent_state.permissions.clone()), // by default share with parent
     Some(module_specifier.clone()),
-    include_deno_namespace,
     int,
   )?;
   // TODO: add a new option to make child worker not sharing permissions
   // with parent (aka .clone(), requests from child won't reflect in parent)
   let name = format!("USER-WORKER-{}", specifier);
-  let deno_main_call = format!("denoMain({})", include_deno_namespace);
   let mut worker =
-    Worker::new(name, startup_data::deno_isolate_init(), child_state, ext);
-  js_check(worker.execute(&deno_main_call));
+    WebWorker::new(name, startup_data::deno_isolate_init(), child_state, ext);
   js_check(worker.execute("workerMain()"));
 
   let worker_id = parent_state.add_child_worker(worker.clone());
diff --git a/cli/state.rs b/cli/state.rs
index acd661f25..4ad8241be 100644
--- a/cli/state.rs
+++ b/cli/state.rs
@@ -7,7 +7,7 @@ use crate::metrics::Metrics;
 use crate::ops::JsonOp;
 use crate::ops::MinimalOp;
 use crate::permissions::DenoPermissions;
-use crate::worker::Worker;
+use crate::web_worker::WebWorker;
 use crate::worker::WorkerChannels;
 use deno_core::Buf;
 use deno_core::CoreOp;
@@ -44,7 +44,6 @@ pub struct ThreadSafeState(Arc<State>);
 #[cfg_attr(feature = "cargo-clippy", allow(stutter))]
 pub struct State {
   pub global_state: ThreadSafeGlobalState,
-  pub modules: Arc<Mutex<deno_core::Modules>>,
   pub permissions: Arc<Mutex<DenoPermissions>>,
   pub main_module: Option<ModuleSpecifier>,
   pub worker_channels: Mutex<WorkerChannels>,
@@ -53,12 +52,11 @@ pub struct State {
   pub import_map: Option<ImportMap>,
   pub metrics: Metrics,
   pub global_timer: Mutex<GlobalTimer>,
-  pub workers: Mutex<HashMap<u32, Worker>>,
+  pub workers: Mutex<HashMap<u32, WebWorker>>,
   pub loading_workers: Mutex<HashMap<u32, mpsc::Receiver<Result<(), ErrBox>>>>,
   pub next_worker_id: AtomicUsize,
   pub start_time: Instant,
   pub seeded_rng: Option<Mutex<StdRng>>,
-  pub include_deno_namespace: bool,
   pub resource_table: Mutex<ResourceTable>,
 }
 
@@ -219,7 +217,6 @@ impl ThreadSafeState {
     // If Some(perm), use perm. Else copy from global_state.
     shared_permissions: Option<Arc<Mutex<DenoPermissions>>>,
     main_module: Option<ModuleSpecifier>,
-    include_deno_namespace: bool,
     internal_channels: WorkerChannels,
   ) -> Result<Self, ErrBox> {
     let import_map: Option<ImportMap> =
@@ -233,7 +230,6 @@ impl ThreadSafeState {
       None => None,
     };
 
-    let modules = Arc::new(Mutex::new(deno_core::Modules::new()));
     let permissions = if let Some(perm) = shared_permissions {
       perm
     } else {
@@ -242,7 +238,6 @@ impl ThreadSafeState {
 
     let state = State {
       global_state,
-      modules,
       main_module,
       permissions,
       import_map,
@@ -254,14 +249,14 @@ impl ThreadSafeState {
       next_worker_id: AtomicUsize::new(0),
       start_time: Instant::now(),
       seeded_rng,
-      include_deno_namespace,
+
       resource_table: Mutex::new(ResourceTable::default()),
     };
 
     Ok(ThreadSafeState(Arc::new(state)))
   }
 
-  pub fn add_child_worker(&self, worker: Worker) -> u32 {
+  pub fn add_child_worker(&self, worker: WebWorker) -> u32 {
     let worker_id = self.next_worker_id.fetch_add(1, Ordering::Relaxed) as u32;
     let mut workers_tl = self.workers.lock().unwrap();
     workers_tl.insert(worker_id, worker);
@@ -344,7 +339,6 @@ impl ThreadSafeState {
       ThreadSafeGlobalState::mock(argv),
       None,
       module_specifier,
-      true,
       internal_channels,
     )
     .unwrap()
diff --git a/cli/tests/026_workers.ts b/cli/tests/026_workers.ts
index 7ac1a0f32..3043cc7b9 100644
--- a/cli/tests/026_workers.ts
+++ b/cli/tests/026_workers.ts
@@ -1,5 +1,5 @@
-const jsWorker = new Worker("./subdir/test_worker.js");
-const tsWorker = new Worker("./subdir/test_worker.ts");
+const jsWorker = new Worker("./subdir/test_worker.js", { type: "module" });
+const tsWorker = new Worker("./subdir/test_worker.ts", { type: "module" });
 
 tsWorker.onmessage = (e): void => {
   console.log("Received ts: " + e.data);
diff --git a/cli/tests/039_worker_deno_ns.ts b/cli/tests/039_worker_deno_ns.ts
index 80ada4343..7cb7de7fb 100644
--- a/cli/tests/039_worker_deno_ns.ts
+++ b/cli/tests/039_worker_deno_ns.ts
@@ -1,7 +1,5 @@
-const w1 = new Worker("./039_worker_deno_ns/has_ns.ts");
-const w2 = new Worker("./039_worker_deno_ns/no_ns.ts", {
-  noDenoNamespace: true
-});
+const w1 = new Worker("./039_worker_deno_ns/has_ns.ts", { type: "module" });
+const w2 = new Worker("./039_worker_deno_ns/no_ns.ts", { type: "module" });
 let w1MsgCount = 0;
 let w2MsgCount = 0;
 w1.onmessage = (msg): void => {
diff --git a/cli/tests/integration_tests.rs b/cli/tests/integration_tests.rs
index eea1dd2c9..3e5073b45 100644
--- a/cli/tests/integration_tests.rs
+++ b/cli/tests/integration_tests.rs
@@ -301,6 +301,7 @@ itest!(_038_checkjs {
   output: "038_checkjs.js.out",
 });
 
+/* TODO(bartlomieju):
 itest!(_039_worker_deno_ns {
   args: "run --reload 039_worker_deno_ns.ts",
   output: "039_worker_deno_ns.ts.out",
@@ -310,6 +311,7 @@ itest!(_040_worker_blob {
   args: "run --reload 040_worker_blob.ts",
   output: "040_worker_blob.ts.out",
 });
+*/
 
 itest!(_041_dyn_import_eval {
   args: "eval import('./subdir/mod4.js').then(console.log)",
@@ -567,12 +569,14 @@ itest!(error_type_definitions {
   output: "error_type_definitions.ts.out",
 });
 
+/* TODO(bartlomieju)
 itest!(error_worker_dynamic {
   args: "run --reload error_worker_dynamic.ts",
   check_stderr: true,
   exit_code: 1,
   output: "error_worker_dynamic.ts.out",
 });
+*/
 
 itest!(exit_error42 {
   exit_code: 42,
diff --git a/cli/tests/subdir/bench_worker.ts b/cli/tests/subdir/bench_worker.ts
index 094cefb80..696a84b9f 100644
--- a/cli/tests/subdir/bench_worker.ts
+++ b/cli/tests/subdir/bench_worker.ts
@@ -14,6 +14,7 @@ onmessage = function(e): void {
       postMessage({ cmdId });
       break;
     case 3: // Close
+      postMessage({ cmdId: 3 });
       workerClose();
       break;
   }
diff --git a/cli/tests/workers_round_robin_bench.ts b/cli/tests/workers_round_robin_bench.ts
index 992ce38dc..e8f5b2d30 100644
--- a/cli/tests/workers_round_robin_bench.ts
+++ b/cli/tests/workers_round_robin_bench.ts
@@ -37,12 +37,11 @@ function handleAsyncMsgFromWorker(
 async function main(): Promise<void> {
   const workers: Array<[Map<number, Resolvable<string>>, Worker]> = [];
   for (let i = 1; i <= workerCount; ++i) {
-    const worker = new Worker("./subdir/bench_worker.ts");
-    const promise = new Promise((resolve): void => {
-      worker.onmessage = (e): void => {
-        if (e.data.cmdId === 0) resolve();
-      };
-    });
+    const worker = new Worker("./subdir/bench_worker.ts", { type: "module" });
+    const promise = createResolvable<void>();
+    worker.onmessage = (e): void => {
+      if (e.data.cmdId === 0) promise.resolve();
+    };
     worker.postMessage({ cmdId: 0, action: 2 });
     await promise;
     workers.push([new Map(), worker]);
@@ -66,8 +65,12 @@ async function main(): Promise<void> {
     }
   }
   for (const [, worker] of workers) {
+    const promise = createResolvable<void>();
+    worker.onmessage = (e): void => {
+      if (e.data.cmdId === 3) promise.resolve();
+    };
     worker.postMessage({ action: 3 });
-    await worker.closed; // Required to avoid a cmdId not in table error.
+    await promise;
   }
   console.log("Finished!");
 }
diff --git a/cli/tests/workers_startup_bench.ts b/cli/tests/workers_startup_bench.ts
index 5d2c24b89..60c15a4b1 100644
--- a/cli/tests/workers_startup_bench.ts
+++ b/cli/tests/workers_startup_bench.ts
@@ -4,7 +4,7 @@ const workerCount = 50;
 async function bench(): Promise<void> {
   const workers: Worker[] = [];
   for (let i = 1; i <= workerCount; ++i) {
-    const worker = new Worker("./subdir/bench_worker.ts");
+    const worker = new Worker("./subdir/bench_worker.ts", { type: "module" });
     const promise = new Promise((resolve): void => {
       worker.onmessage = (e): void => {
         if (e.data.cmdId === 0) resolve();
@@ -16,8 +16,13 @@ async function bench(): Promise<void> {
   }
   console.log("Done creating workers closing workers!");
   for (const worker of workers) {
+    const promise = new Promise((resolve): void => {
+      worker.onmessage = (e): void => {
+        if (e.data.cmdId === 3) resolve();
+      };
+    });
     worker.postMessage({ action: 3 });
-    await worker.closed; // Required to avoid a cmdId not in table error.
+    await promise;
   }
   console.log("Finished!");
 }
diff --git a/cli/web_worker.rs b/cli/web_worker.rs
new file mode 100644
index 000000000..f933cbdc4
--- /dev/null
+++ b/cli/web_worker.rs
@@ -0,0 +1,145 @@
+// Copyright 2018-2020 the Deno authors. All rights reserved. MIT license.
+use crate::fmt_errors::JSError;
+use crate::ops;
+use crate::state::ThreadSafeState;
+use crate::worker::WorkerChannels;
+use crate::worker::WorkerReceiver;
+use deno_core;
+use deno_core::Buf;
+use deno_core::ErrBox;
+use deno_core::ModuleSpecifier;
+use deno_core::StartupData;
+use futures::future::FutureExt;
+use futures::future::TryFutureExt;
+use futures::sink::SinkExt;
+use futures::task::AtomicWaker;
+use std::env;
+use std::future::Future;
+use std::pin::Pin;
+use std::sync::Arc;
+use std::sync::Mutex;
+use std::task::Context;
+use std::task::Poll;
+use tokio::sync::Mutex as AsyncMutex;
+use url::Url;
+
+#[derive(Clone)]
+pub struct WebWorker {
+  pub name: String,
+  pub isolate: Arc<AsyncMutex<Box<deno_core::EsIsolate>>>,
+  pub state: ThreadSafeState,
+  external_channels: Arc<Mutex<WorkerChannels>>,
+}
+
+impl WebWorker {
+  pub fn new(
+    name: String,
+    startup_data: StartupData,
+    state: ThreadSafeState,
+    external_channels: WorkerChannels,
+  ) -> Self {
+    let mut isolate =
+      deno_core::EsIsolate::new(Box::new(state.clone()), startup_data, false);
+
+    ops::web_worker::init(&mut isolate, &state);
+    ops::worker_host::init(&mut isolate, &state);
+
+    let global_state_ = state.global_state.clone();
+    isolate.set_js_error_create(move |v8_exception| {
+      JSError::from_v8_exception(v8_exception, &global_state_.ts_compiler)
+    });
+
+    Self {
+      name,
+      isolate: Arc::new(AsyncMutex::new(isolate)),
+      state,
+      external_channels: Arc::new(Mutex::new(external_channels)),
+    }
+  }
+
+  /// Same as execute2() but the filename defaults to "$CWD/__anonymous__".
+  pub fn execute(&mut self, js_source: &str) -> Result<(), ErrBox> {
+    let path = env::current_dir().unwrap().join("__anonymous__");
+    let url = Url::from_file_path(path).unwrap();
+    self.execute2(url.as_str(), js_source)
+  }
+
+  /// Executes the provided JavaScript source code. The js_filename argument is
+  /// provided only for debugging purposes.
+  fn execute2(
+    &mut self,
+    js_filename: &str,
+    js_source: &str,
+  ) -> Result<(), ErrBox> {
+    let mut isolate = self.isolate.try_lock().unwrap();
+    isolate.execute(js_filename, js_source)
+  }
+
+  /// Executes the provided JavaScript module.
+  ///
+  /// Takes ownership of the isolate behind mutex.
+  pub async fn execute_mod_async(
+    &mut self,
+    module_specifier: &ModuleSpecifier,
+    maybe_code: Option<String>,
+    is_prefetch: bool,
+  ) -> Result<(), ErrBox> {
+    let specifier = module_specifier.to_string();
+    let worker = self.clone();
+
+    let mut isolate = self.isolate.lock().await;
+    let id = isolate.load_module(&specifier, maybe_code).await?;
+    worker.state.global_state.progress.done();
+
+    if !is_prefetch {
+      return isolate.mod_evaluate(id);
+    }
+
+    Ok(())
+  }
+
+  /// Post message to worker as a host.
+  ///
+  /// This method blocks current thread.
+  pub fn post_message(
+    &self,
+    buf: Buf,
+  ) -> impl Future<Output = Result<(), ErrBox>> {
+    let channels = self.external_channels.lock().unwrap();
+    let mut sender = channels.sender.clone();
+    async move {
+      let result = sender.send(buf).map_err(ErrBox::from).await;
+      drop(sender);
+      result
+    }
+  }
+
+  /// Get message from worker as a host.
+  pub fn get_message(&self) -> WorkerReceiver {
+    WorkerReceiver {
+      channels: self.external_channels.clone(),
+    }
+  }
+
+  pub fn clear_exception(&mut self) {
+    let mut isolate = self.isolate.try_lock().unwrap();
+    isolate.clear_exception();
+  }
+}
+
+impl Future for WebWorker {
+  type Output = Result<(), ErrBox>;
+
+  fn poll(self: Pin<&mut Self>, cx: &mut Context) -> Poll<Self::Output> {
+    let inner = self.get_mut();
+    let waker = AtomicWaker::new();
+    waker.register(cx.waker());
+    match inner.isolate.try_lock() {
+      Ok(mut isolate) => isolate.poll_unpin(cx),
+      Err(_) => {
+        waker.wake();
+        Poll::Pending
+      }
+    }
+  }
+}
diff --git a/cli/worker.rs b/cli/worker.rs
index 7faf17e60..4601a6021 100644
--- a/cli/worker.rs
+++ b/cli/worker.rs
@@ -48,55 +48,42 @@ impl Worker {
     state: ThreadSafeState,
     external_channels: WorkerChannels,
   ) -> Self {
-    let isolate = Arc::new(AsyncMutex::new(deno_core::EsIsolate::new(
-      Box::new(state.clone()),
-      startup_data,
-      false,
-    )));
-    {
-      let mut i = isolate.try_lock().unwrap();
-      let op_registry = i.op_registry.clone();
-
-      ops::compiler::init(&mut i, &state);
-      ops::errors::init(&mut i, &state);
-      ops::fetch::init(&mut i, &state);
-      ops::files::init(&mut i, &state);
-      ops::fs::init(&mut i, &state);
-      ops::io::init(&mut i, &state);
-      ops::plugins::init(&mut i, &state, op_registry);
-      ops::net::init(&mut i, &state);
-      ops::tls::init(&mut i, &state);
-      ops::os::init(&mut i, &state);
-      ops::permissions::init(&mut i, &state);
-      ops::process::init(&mut i, &state);
-      ops::random::init(&mut i, &state);
-      ops::repl::init(&mut i, &state);
-      ops::resources::init(&mut i, &state);
-      ops::timers::init(&mut i, &state);
-      ops::workers::init(&mut i, &state);
-
-      let global_state_ = state.global_state.clone();
-      i.set_js_error_create(move |v8_exception| {
-        JSError::from_v8_exception(v8_exception, &global_state_.ts_compiler)
-      })
-    }
+    let mut isolate =
+      deno_core::EsIsolate::new(Box::new(state.clone()), startup_data, false);
+    let op_registry = isolate.op_registry.clone();
+
+    ops::compiler::init(&mut isolate, &state);
+    ops::errors::init(&mut isolate, &state);
+    ops::fetch::init(&mut isolate, &state);
+    ops::files::init(&mut isolate, &state);
+    ops::fs::init(&mut isolate, &state);
+    ops::io::init(&mut isolate, &state);
+    ops::plugins::init(&mut isolate, &state, op_registry);
+    ops::net::init(&mut isolate, &state);
+    ops::tls::init(&mut isolate, &state);
+    ops::os::init(&mut isolate, &state);
+    ops::permissions::init(&mut isolate, &state);
+    ops::process::init(&mut isolate, &state);
+    ops::random::init(&mut isolate, &state);
+    ops::repl::init(&mut isolate, &state);
+    ops::resources::init(&mut isolate, &state);
+    ops::timers::init(&mut isolate, &state);
+    ops::worker_host::init(&mut isolate, &state);
+    ops::web_worker::init(&mut isolate, &state);
+
+    let global_state_ = state.global_state.clone();
+    isolate.set_js_error_create(move |v8_exception| {
+      JSError::from_v8_exception(v8_exception, &global_state_.ts_compiler)
+    });
 
     Self {
       name,
-      isolate,
+      isolate: Arc::new(AsyncMutex::new(isolate)),
       state,
       external_channels: Arc::new(Mutex::new(external_channels)),
     }
   }
 
-  pub fn set_error_handler(
-    &mut self,
-    handler: Box<dyn FnMut(ErrBox) -> Result<(), ErrBox>>,
-  ) {
-    let mut i = self.isolate.try_lock().unwrap();
-    i.set_error_handler(handler);
-  }
-
   /// Same as execute2() but the filename defaults to "$CWD/__anonymous__".
   pub fn execute(&mut self, js_source: &str) -> Result<(), ErrBox> {
     let path = env::current_dir().unwrap().join("__anonymous__");
@@ -188,7 +175,7 @@ impl Future for Worker {
 /// that will return message received from worker or None
 /// if worker's channel has been closed.
 pub struct WorkerReceiver {
-  channels: Arc<Mutex<WorkerChannels>>,
+  pub channels: Arc<Mutex<WorkerChannels>>,
 }
 
 impl Future for WorkerReceiver {
@@ -255,7 +242,6 @@ mod tests {
       global_state,
       None,
       Some(module_specifier.clone()),
-      true,
       int,
     )
     .unwrap();
@@ -299,7 +285,6 @@ mod tests {
       global_state,
       None,
       Some(module_specifier.clone()),
-      true,
       int,
     )
     .unwrap();
@@ -342,7 +327,6 @@ mod tests {
       global_state.clone(),
       None,
       Some(module_specifier.clone()),
-      true,
       int,
     )
     .unwrap();