Support scoped variables, unblock REPL async op, and REPL error colors (#1721)

18 files changed, 330 insertions, 55 deletions

diff --git a/BUILD.gn b/BUILD.gn
index 239a0f995..4f8550d0d 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -68,6 +68,7 @@ ts_sources = [
   "js/event.ts",
   "js/event_target.ts",
   "js/fetch.ts",
+  "js/format_error.ts",
   "js/dom_file.ts",
   "js/file_info.ts",
   "js/files.ts",
diff --git a/js/console.ts b/js/console.ts
index 0797ab8e9..e5dafceee 100644
--- a/js/console.ts
+++ b/js/console.ts
@@ -3,6 +3,8 @@ import { isTypedArray } from "./util";
 import { TextEncoder } from "./text_encoding";
 import { File, stdout } from "./files";
 import { cliTable } from "./console_table";
+import { formatError } from "./format_error";
+import { libdeno } from "./libdeno";
 
 // tslint:disable-next-line:no-any
 type ConsoleContext = Set<any>;
@@ -263,7 +265,8 @@ function createObjectString(
   ...args: [ConsoleContext, number, number]
 ): string {
   if (value instanceof Error) {
-    return value.stack! || "";
+    const errorJSON = libdeno.errorToJSON(value);
+    return formatError(errorJSON);
   } else if (Array.isArray(value)) {
     return createArrayString(value, ...args);
   } else if (value instanceof Number) {
diff --git a/js/console_test.ts b/js/console_test.ts
index 577c8bf5d..f84dc247a 100644
--- a/js/console_test.ts
+++ b/js/console_test.ts
@@ -1,6 +1,6 @@
 // Copyright 2018-2019 the Deno authors. All rights reserved. MIT license.
 import { Console, libdeno, stringifyArgs, inspect, write, stdout } from "deno";
-import { test, assertEqual } from "./test_util.ts";
+import { test, assertEqual, assert } from "./test_util.ts";
 
 const console = new Console(libdeno.print);
 
@@ -245,7 +245,8 @@ test(function consoleTestError() {
   try {
     throw new MyError("This is an error");
   } catch (e) {
-    assertEqual(stringify(e).split("\n")[0], "MyError: This is an error");
+    assert(stringify(e).split("\n")[3]
+      .includes("MyError: This is an error"));
   }
 });
 
diff --git a/js/format_error.ts b/js/format_error.ts
new file mode 100644
index 000000000..ebc579355
--- /dev/null
+++ b/js/format_error.ts
@@ -0,0 +1,21 @@
+// Copyright 2018-2019 the Deno authors. All rights reserved. MIT license.
+import * as msg from "gen/msg_generated";
+import * as flatbuffers from "./flatbuffers";
+import { sendSync } from "./dispatch";
+import { assert } from "./util";
+
+export function formatError(errString: string): string {
+  const builder = flatbuffers.createBuilder();
+  const errString_ = builder.createString(errString);
+  msg.FormatError.startFormatError(builder);
+  msg.FormatError.addError(builder, errString_);
+  const offset = msg.FormatError.endFormatError(builder);
+  const baseRes = sendSync(builder, msg.Any.FormatError, offset);
+  assert(baseRes != null);
+  assert(msg.Any.FormatErrorRes === baseRes!.innerType());
+  const formatErrorResMsg = new msg.FormatErrorRes();
+  assert(baseRes!.inner(formatErrorResMsg) != null);
+  const formattedError = formatErrorResMsg.error();
+  assert(formatError != null);
+  return formattedError!;
+}
diff --git a/js/libdeno.ts b/js/libdeno.ts
index 401ffae40..7d2bc3ede 100644
--- a/js/libdeno.ts
+++ b/js/libdeno.ts
@@ -3,11 +3,17 @@ import { globalEval } from "./global_eval";
 
 // The libdeno functions are moved so that users can't access them.
 type MessageCallback = (msg: Uint8Array) => void;
-export type PromiseRejectEvent =
-  | "RejectWithNoHandler"
-  | "HandlerAddedAfterReject"
-  | "ResolveAfterResolved"
-  | "RejectAfterResolved";
+
+interface EvalErrorInfo {
+  // Is the object thrown a native Error?
+  isNativeError: boolean;
+  // Was the error happened during compilation?
+  isCompileError: boolean;
+  // The actual thrown entity
+  // (might be an Error or anything else thrown by the user)
+  // If isNativeError is true, this is an Error
+  thrown: any; // tslint:disable-line:no-any
+}
 
 interface Libdeno {
   recv(cb: MessageCallback): void;
@@ -20,26 +26,17 @@ interface Libdeno {
 
   builtinModules: { [s: string]: object };
 
-  setGlobalErrorHandler: (
-    handler: (
-      message: string,
-      source: string,
-      line: number,
-      col: number,
-      error: Error
-    ) => void
-  ) => void;
-
-  setPromiseRejectHandler: (
-    handler: (
-      error: Error | string,
-      event: PromiseRejectEvent,
-      /* tslint:disable-next-line:no-any */
-      promise: Promise<any>
-    ) => void
-  ) => void;
-
-  setPromiseErrorExaminer: (handler: () => boolean) => void;
+  /** Evaluate provided code in the current context.
+   * It differs from eval(...) in that it does not create a new context.
+   * Returns an array: [output, errInfo].
+   * If an error occurs, `output` becomes null and `errInfo` is non-null.
+   */
+  evalContext(
+    code: string
+  ): [any, EvalErrorInfo | null] /* tslint:disable-line:no-any */;
+
+  // tslint:disable-next-line:no-any
+  errorToJSON: (e: Error) => string;
 }
 
 const window = globalEval("this");
diff --git a/js/repl.ts b/js/repl.ts
index 6fb395e1b..6676721fc 100644
--- a/js/repl.ts
+++ b/js/repl.ts
@@ -7,6 +7,8 @@ import { close } from "./files";
 import * as dispatch from "./dispatch";
 import { exit } from "./os";
 import { globalEval } from "./global_eval";
+import { libdeno } from "./libdeno";
+import { formatError } from "./format_error";
 
 const window = globalEval("this");
 
@@ -96,14 +98,19 @@ export async function replLoop(): Promise<void> {
 }
 
 function evaluate(code: string): void {
-  try {
-    const result = eval.call(window, code); // FIXME use a new scope.
+  if (code.trim() === "") {
+    return;
+  }
+  const [result, errInfo] = libdeno.evalContext(code);
+  if (!errInfo) {
     console.log(result);
-  } catch (err) {
-    if (err instanceof Error) {
-      console.error(`${err.constructor.name}: ${err.message}`);
+  } else {
+    if (errInfo.isNativeError) {
+      const formattedError = formatError(
+        libdeno.errorToJSON(errInfo.thrown as Error));
+      console.error(formattedError);
     } else {
-      console.error("Thrown:", err);
+      console.error("Thrown:", errInfo.thrown);
     }
   }
 }
diff --git a/libdeno/api.cc b/libdeno/api.cc
index e540c95fc..21ece13a6 100644
--- a/libdeno/api.cc
+++ b/libdeno/api.cc
@@ -9,6 +9,7 @@
 #include "third_party/v8/src/base/logging.h"
 
 #include "deno.h"
+#include "exceptions.h"
 #include "internal.h"
 
 extern "C" {
diff --git a/libdeno/binding.cc b/libdeno/binding.cc
index 78e4cad29..f7ee977e8 100644
--- a/libdeno/binding.cc
+++ b/libdeno/binding.cc
@@ -120,6 +120,16 @@ void Print(const v8::FunctionCallbackInfo<v8::Value>& args) {
   fflush(file);
 }
 
+void ErrorToJSON(const v8::FunctionCallbackInfo<v8::Value>& args) {
+  CHECK_EQ(args.Length(), 1);
+  auto* isolate = args.GetIsolate();
+  DenoIsolate* d = DenoIsolate::FromIsolate(isolate);
+  auto context = d->context_.Get(d->isolate_);
+  v8::HandleScope handle_scope(isolate);
+  auto json_string = EncodeExceptionAsJSON(context, args[0]);
+  args.GetReturnValue().Set(v8_str(json_string.c_str()));
+}
+
 v8::Local<v8::Uint8Array> ImportBuf(DenoIsolate* d, deno_buf buf) {
   if (buf.alloc_ptr == nullptr) {
     // If alloc_ptr isn't set, we memcpy.
@@ -368,6 +378,80 @@ bool Execute(v8::Local<v8::Context> context, const char* js_filename,
   return true;
 }
 
+static inline v8::Local<v8::Boolean> v8_bool(bool v) {
+  return v8::Boolean::New(v8::Isolate::GetCurrent(), v);
+}
+
+void EvalContext(const v8::FunctionCallbackInfo<v8::Value>& args) {
+  v8::Isolate* isolate = args.GetIsolate();
+  DenoIsolate* d = DenoIsolate::FromIsolate(isolate);
+  v8::EscapableHandleScope handleScope(isolate);
+  auto context = d->context_.Get(isolate);
+  v8::Context::Scope context_scope(context);
+
+  CHECK(args[0]->IsString());
+  auto source = args[0].As<v8::String>();
+
+  auto output = v8::Array::New(isolate, 2);
+  /**
+   * output[0] = result
+   * output[1] = ErrorInfo | null
+   *   ErrorInfo = {
+   *     thrown: Error | any,
+   *     isNativeError: boolean,
+   *     isCompileError: boolean,
+   *   }
+   */
+
+  v8::TryCatch try_catch(isolate);
+
+  auto name = v8_str("<unknown>");
+  v8::ScriptOrigin origin(name);
+  auto script = v8::Script::Compile(context, source, &origin);
+
+  if (script.IsEmpty()) {
+    DCHECK(try_catch.HasCaught());
+    auto exception = try_catch.Exception();
+
+    output->Set(0, v8::Null(isolate));
+
+    auto errinfo_obj = v8::Object::New(isolate);
+    errinfo_obj->Set(v8_str("isCompileError"), v8_bool(true));
+    errinfo_obj->Set(v8_str("isNativeError"),
+                     v8_bool(exception->IsNativeError()));
+    errinfo_obj->Set(v8_str("thrown"), exception);
+
+    output->Set(1, errinfo_obj);
+
+    args.GetReturnValue().Set(output);
+    return;
+  }
+
+  auto result = script.ToLocalChecked()->Run(context);
+
+  if (result.IsEmpty()) {
+    DCHECK(try_catch.HasCaught());
+    auto exception = try_catch.Exception();
+
+    output->Set(0, v8::Null(isolate));
+
+    auto errinfo_obj = v8::Object::New(isolate);
+    errinfo_obj->Set(v8_str("isCompileError"), v8_bool(false));
+    errinfo_obj->Set(v8_str("isNativeError"),
+                     v8_bool(exception->IsNativeError()));
+    errinfo_obj->Set(v8_str("thrown"), exception);
+
+    output->Set(1, errinfo_obj);
+
+    args.GetReturnValue().Set(output);
+    return;
+  }
+
+  output->Set(0, result.ToLocalChecked());
+  output->Set(1, v8::Null(isolate));
+  args.GetReturnValue().Set(output);
+}
+
 void InitializeContext(v8::Isolate* isolate, v8::Local<v8::Context> context) {
   v8::HandleScope handle_scope(isolate);
   v8::Context::Scope context_scope(context);
@@ -389,6 +473,18 @@ void InitializeContext(v8::Isolate* isolate, v8::Local<v8::Context> context) {
   auto send_val = send_tmpl->GetFunction(context).ToLocalChecked();
   CHECK(deno_val->Set(context, deno::v8_str("send"), send_val).FromJust());
 
+  auto eval_context_tmpl = v8::FunctionTemplate::New(isolate, EvalContext);
+  auto eval_context_val =
+      eval_context_tmpl->GetFunction(context).ToLocalChecked();
+  CHECK(deno_val->Set(context, deno::v8_str("evalContext"), eval_context_val)
+            .FromJust());
+
+  auto error_to_json_tmpl = v8::FunctionTemplate::New(isolate, ErrorToJSON);
+  auto error_to_json_val =
+      error_to_json_tmpl->GetFunction(context).ToLocalChecked();
+  CHECK(deno_val->Set(context, deno::v8_str("errorToJSON"), error_to_json_val)
+            .FromJust());
+
   CHECK(deno_val->SetAccessor(context, deno::v8_str("shared"), Shared)
             .FromJust());
 
diff --git a/libdeno/exceptions.cc b/libdeno/exceptions.cc
index 0d7bbed8b..51f81bfce 100644
--- a/libdeno/exceptions.cc
+++ b/libdeno/exceptions.cc
@@ -4,10 +4,10 @@
 
 namespace deno {
 
-std::string EncodeMessageAsJSON(v8::Local<v8::Context> context,
-                                v8::Local<v8::Message> message) {
+v8::Local<v8::Object> EncodeMessageAsObject(v8::Local<v8::Context> context,
+                                            v8::Local<v8::Message> message) {
   auto* isolate = context->GetIsolate();
-  v8::HandleScope handle_scope(isolate);
+  v8::EscapableHandleScope handle_scope(isolate);
   v8::Context::Scope context_scope(context);
 
   auto stack_trace = message->GetStackTrace();
@@ -134,12 +134,33 @@ std::string EncodeMessageAsJSON(v8::Local<v8::Context> context,
   }
 
   CHECK(json_obj->Set(context, v8_str("frames"), frames).FromJust());
+  json_obj = handle_scope.Escape(json_obj);
+  return json_obj;
+}
 
+std::string EncodeMessageAsJSON(v8::Local<v8::Context> context,
+                                v8::Local<v8::Message> message) {
+  auto* isolate = context->GetIsolate();
+  v8::HandleScope handle_scope(isolate);
+  v8::Context::Scope context_scope(context);
+  auto json_obj = EncodeMessageAsObject(context, message);
   auto json_string = v8::JSON::Stringify(context, json_obj).ToLocalChecked();
   v8::String::Utf8Value json_string_(isolate, json_string);
   return std::string(ToCString(json_string_));
 }
 
+v8::Local<v8::Object> EncodeExceptionAsObject(v8::Local<v8::Context> context,
+                                              v8::Local<v8::Value> exception) {
+  auto* isolate = context->GetIsolate();
+  v8::EscapableHandleScope handle_scope(isolate);
+  v8::Context::Scope context_scope(context);
+
+  auto message = v8::Exception::CreateMessage(isolate, exception);
+  auto json_obj = EncodeMessageAsObject(context, message);
+  json_obj = handle_scope.Escape(json_obj);
+  return json_obj;
+}
+
 std::string EncodeExceptionAsJSON(v8::Local<v8::Context> context,
                                   v8::Local<v8::Value> exception) {
   auto* isolate = context->GetIsolate();
@@ -167,5 +188,4 @@ void HandleExceptionMessage(v8::Local<v8::Context> context,
   CHECK_NOT_NULL(d);
   d->last_exception_ = json_str;
 }
-
 }  // namespace deno
diff --git a/libdeno/exceptions.h b/libdeno/exceptions.h
index 362bbc0e6..e07ff183a 100644
--- a/libdeno/exceptions.h
+++ b/libdeno/exceptions.h
@@ -2,10 +2,17 @@
 #ifndef EXCEPTIONS_H_
 #define EXCEPTIONS_H_
 
+#include <string>
 #include "third_party/v8/include/v8.h"
 
 namespace deno {
 
+v8::Local<v8::Object> EncodeExceptionAsObject(v8::Local<v8::Context> context,
+                                              v8::Local<v8::Value> exception);
+
+std::string EncodeExceptionAsJSON(v8::Local<v8::Context> context,
+                                  v8::Local<v8::Value> exception);
+
 void HandleException(v8::Local<v8::Context> context,
                      v8::Local<v8::Value> exception);
 
diff --git a/libdeno/internal.h b/libdeno/internal.h
index 0cd50162c..a87ec0fdc 100644
--- a/libdeno/internal.h
+++ b/libdeno/internal.h
@@ -133,6 +133,8 @@ static inline v8::Local<v8::String> v8_str(const char* x) {
 void Print(const v8::FunctionCallbackInfo<v8::Value>& args);
 void Recv(const v8::FunctionCallbackInfo<v8::Value>& args);
 void Send(const v8::FunctionCallbackInfo<v8::Value>& args);
+void EvalContext(const v8::FunctionCallbackInfo<v8::Value>& args);
+void ErrorToJSON(const v8::FunctionCallbackInfo<v8::Value>& args);
 void Shared(v8::Local<v8::Name> property,
             const v8::PropertyCallbackInfo<v8::Value>& info);
 void BuiltinModules(v8::Local<v8::Name> property,
@@ -142,6 +144,8 @@ static intptr_t external_references[] = {
     reinterpret_cast<intptr_t>(Print),
     reinterpret_cast<intptr_t>(Recv),
     reinterpret_cast<intptr_t>(Send),
+    reinterpret_cast<intptr_t>(EvalContext),
+    reinterpret_cast<intptr_t>(ErrorToJSON),
     reinterpret_cast<intptr_t>(Shared),
     reinterpret_cast<intptr_t>(BuiltinModules),
     reinterpret_cast<intptr_t>(MessageCallback),
@@ -153,9 +157,6 @@ Deno* NewFromSnapshot(void* user_data, deno_recv_cb cb);
 
 void InitializeContext(v8::Isolate* isolate, v8::Local<v8::Context> context);
 
-void HandleException(v8::Local<v8::Context> context,
-                     v8::Local<v8::Value> exception);
-
 void DeserializeInternalFields(v8::Local<v8::Object> holder, int index,
                                v8::StartupData payload, void* data);
 
diff --git a/libdeno/libdeno_test.cc b/libdeno/libdeno_test.cc
index 0936c53b4..3193e7677 100644
--- a/libdeno/libdeno_test.cc
+++ b/libdeno/libdeno_test.cc
@@ -290,6 +290,20 @@ TEST(LibDenoTest, Utf8Bug) {
   deno_delete(d);
 }
 
+TEST(LibDenoTest, LibDenoEvalContext) {
+  Deno* d = deno_new(deno_config{0, snapshot, empty, nullptr});
+  deno_execute(d, nullptr, "a.js", "LibDenoEvalContext();");
+  EXPECT_EQ(nullptr, deno_last_exception(d));
+  deno_delete(d);
+}
+
+TEST(LibDenoTest, LibDenoEvalContextError) {
+  Deno* d = deno_new(deno_config{0, snapshot, empty, nullptr});
+  deno_execute(d, nullptr, "a.js", "LibDenoEvalContextError();");
+  EXPECT_EQ(nullptr, deno_last_exception(d));
+  deno_delete(d);
+}
+
 TEST(LibDenoTest, SharedAtomics) {
   int32_t s[] = {0, 1, 2};
   deno_buf shared = {nullptr, 0, reinterpret_cast<uint8_t*>(s), sizeof s};
diff --git a/libdeno/libdeno_test.js b/libdeno/libdeno_test.js
index 50f5c03d4..d6ea5f983 100644
--- a/libdeno/libdeno_test.js
+++ b/libdeno/libdeno_test.js
@@ -147,3 +147,50 @@ global.Shared = () => {
   ui8[1] = 43;
   ui8[2] = 44;
 };
+
+global.LibDenoEvalContext = () => {
+  const [result, errInfo] = libdeno.evalContext("let a = 1; a");
+  assert(result === 1);
+  assert(!errInfo);
+  const [result2, errInfo2] = libdeno.evalContext("a = a + 1; a");
+  assert(result2 === 2);
+  assert(!errInfo2);
+};
+
+global.LibDenoEvalContextError = () => {
+  const [result, errInfo] = libdeno.evalContext("not_a_variable");
+  assert(!result);
+  assert(!!errInfo);
+  assert(errInfo.isNativeError); // is a native error (ReferenceError)
+  assert(!errInfo.isCompileError); // is NOT a compilation error
+  assert(errInfo.thrown.message === "not_a_variable is not defined");
+
+  const [result2, errInfo2] = libdeno.evalContext("throw 1");
+  assert(!result2);
+  assert(!!errInfo2);
+  assert(!errInfo2.isNativeError); // is NOT a native error
+  assert(!errInfo2.isCompileError); // is NOT a compilation error
+  assert(errInfo2.thrown === 1);
+
+  const [result3, errInfo3] =
+  libdeno.evalContext("class AError extends Error {}; throw new AError('e')");
+  assert(!result3);
+  assert(!!errInfo3);
+  assert(errInfo3.isNativeError); // extend from native error, still native error
+  assert(!errInfo3.isCompileError); // is NOT a compilation error
+  assert(errInfo3.thrown.message === "e");
+
+  const [result4, errInfo4] = libdeno.evalContext("{");
+  assert(!result4);
+  assert(!!errInfo4);
+  assert(errInfo4.isNativeError); // is a native error (SyntaxError)
+  assert(errInfo4.isCompileError); // is a compilation error! (braces not closed)
+  assert(errInfo4.thrown.message === "Unexpected end of input");
+
+  const [result5, errInfo5] = libdeno.evalContext("eval('{')");
+  assert(!result5);
+  assert(!!errInfo5);
+  assert(errInfo5.isNativeError); // is a native error (SyntaxError)
+  assert(!errInfo5.isCompileError); // is NOT a compilation error! (just eval)
+  assert(errInfo5.thrown.message === "Unexpected end of input");
+};
diff --git a/src/libdeno.rs b/src/libdeno.rs
index ddf025aba..a3a711b65 100644
--- a/src/libdeno.rs
+++ b/src/libdeno.rs
@@ -178,5 +178,4 @@ extern "C" {
     user_data: *const c_void,
     id: deno_mod,
   );
-
 }
diff --git a/src/msg.fbs b/src/msg.fbs
index de69c31ad..7d8b89175 100644
--- a/src/msg.fbs
+++ b/src/msg.fbs
@@ -1,6 +1,8 @@
 union Any {
   Start,
   StartRes,
+  FormatError,
+  FormatErrorRes,
   WorkerGetMessage,
   WorkerGetMessageRes,
   WorkerPostMessage,
@@ -163,6 +165,14 @@ table StartRes {
   no_color: bool;
 }
 
+table FormatError {
+  error: string;
+}
+
+table FormatErrorRes {
+  error: string;
+}
+
 table WorkerGetMessage {
   unused: int8;
 }
diff --git a/src/ops.rs b/src/ops.rs
index 2b4136208..a0646e923 100644
--- a/src/ops.rs
+++ b/src/ops.rs
@@ -10,6 +10,7 @@ use crate::isolate::Buf;
 use crate::isolate::Isolate;
 use crate::isolate::IsolateState;
 use crate::isolate::Op;
+use crate::js_errors::JSError;
 use crate::libdeno;
 use crate::msg;
 use crate::msg_util;
@@ -97,6 +98,7 @@ pub fn dispatch(
       msg::Any::Environ => op_env,
       msg::Any::Exit => op_exit,
       msg::Any::Fetch => op_fetch,
+      msg::Any::FormatError => op_format_error,
       msg::Any::Listen => op_listen,
       msg::Any::MakeTempDir => op_make_temp_dir,
       msg::Any::Metrics => op_metrics,
@@ -283,6 +285,41 @@ fn op_start(
   ))
 }
 
+fn op_format_error(
+  state: &Arc<IsolateState>,
+  base: &msg::Base<'_>,
+  data: libdeno::deno_buf,
+) -> Box<Op> {
+  assert_eq!(data.len(), 0);
+  let inner = base.inner_as_format_error().unwrap();
+  let orig_error = String::from(inner.error().unwrap());
+
+  let js_error = JSError::from_v8_exception(&orig_error).unwrap();
+  let js_error_mapped = js_error.apply_source_map(&state.dir);
+  let js_error_string = js_error_mapped.to_string();
+
+  let mut builder = FlatBufferBuilder::new();
+  let new_error = builder.create_string(&js_error_string);
+
+  let inner = msg::FormatErrorRes::create(
+    &mut builder,
+    &msg::FormatErrorResArgs {
+      error: Some(new_error),
+      ..Default::default()
+    },
+  );
+
+  ok_future(serialize_response(
+    base.cmd_id(),
+    &mut builder,
+    msg::BaseArgs {
+      inner_type: msg::Any::FormatErrorRes,
+      inner: Some(inner.as_union_value()),
+      ..Default::default()
+    },
+  ))
+}
+
 fn serialize_response(
   cmd_id: u32,
   builder: &mut FlatBufferBuilder<'_>,
@@ -1271,7 +1308,8 @@ fn op_repl_readline(
   debug!("op_repl_readline {} {}", rid, prompt);
 
   blocking(base.sync(), move || -> OpResult {
-    let line = resources::readline(rid, &prompt)?;
+    let repl = resources::get_repl(rid)?;
+    let line = repl.lock().unwrap().readline(&prompt)?;
 
     let builder = &mut FlatBufferBuilder::new();
     let line_off = builder.create_string(&line);
diff --git a/src/resources.rs b/src/resources.rs
index 1f5a121de..59167275b 100644
--- a/src/resources.rs
+++ b/src/resources.rs
@@ -35,7 +35,7 @@ use std::net::{Shutdown, SocketAddr};
 use std::process::ExitStatus;
 use std::sync::atomic::AtomicUsize;
 use std::sync::atomic::Ordering;
-use std::sync::Mutex;
+use std::sync::{Arc, Mutex};
 use tokio;
 use tokio::io::{AsyncRead, AsyncWrite};
 use tokio::net::TcpStream;
@@ -95,7 +95,7 @@ enum Repr {
   TcpListener(tokio::net::TcpListener, Option<futures::task::Task>),
   TcpStream(tokio::net::TcpStream),
   HttpBody(HttpBody),
-  Repl(Repl),
+  Repl(Arc<Mutex<Repl>>),
   // Enum size is bounded by the largest variant.
   // Use `Box` around large `Child` struct.
   // https://rust-lang.github.io/rust-clippy/master/index.html#large_enum_variant
@@ -334,7 +334,7 @@ pub fn add_hyper_body(body: hyper::Body) -> Resource {
 pub fn add_repl(repl: Repl) -> Resource {
   let rid = new_rid();
   let mut tg = RESOURCE_TABLE.lock().unwrap();
-  let r = tg.insert(rid, Repr::Repl(repl));
+  let r = tg.insert(rid, Repr::Repl(Arc::new(Mutex::new(repl))));
   assert!(r.is_none());
   Resource { rid }
 }
@@ -462,14 +462,11 @@ pub fn child_status(rid: ResourceId) -> DenoResult<ChildStatus> {
   }
 }
 
-pub fn readline(rid: ResourceId, prompt: &str) -> DenoResult<String> {
+pub fn get_repl(rid: ResourceId) -> DenoResult<Arc<Mutex<Repl>>> {
   let mut table = RESOURCE_TABLE.lock().unwrap();
   let maybe_repr = table.get_mut(&rid);
   match maybe_repr {
-    Some(Repr::Repl(ref mut r)) => {
-      let line = r.readline(&prompt)?;
-      Ok(line)
-    }
+    Some(Repr::Repl(ref mut r)) => Ok(r.clone()),
     _ => Err(bad_resource()),
   }
 }
diff --git a/tools/repl_test.py b/tools/repl_test.py
index 1b589de67..2ce692b99 100644
--- a/tools/repl_test.py
+++ b/tools/repl_test.py
@@ -19,7 +19,7 @@ class Repl(object):
     def input(self, *lines, **kwargs):
         exit_ = kwargs.pop("exit", True)
         sleep_ = kwargs.pop("sleep", 0)
-        p = Popen([self.deno_exe], stdout=PIPE, stderr=PIPE, stdin=PIPE)
+        p = Popen([self.deno_exe, "-A"], stdout=PIPE, stderr=PIPE, stdin=PIPE)
         try:
             # Note: The repl takes a >100ms until it's ready.
             time.sleep(sleep_)
@@ -87,7 +87,7 @@ class Repl(object):
     def test_reference_error(self):
         out, err, code = self.input("not_a_variable")
         assertEqual(out, '')
-        assertEqual(err, 'ReferenceError: not_a_variable is not defined\n')
+        assert "not_a_variable is not defined" in err
         assertEqual(code, 0)
 
     def test_set_timeout(self):
@@ -108,16 +108,25 @@ class Repl(object):
         assertEqual(err, '')
         assertEqual(code, 0)
 
+    def test_async_op(self):
+        out, err, code = self.input(
+            "fetch('http://localhost:4545/tests/001_hello.js')" +
+            ".then(res => res.text()).then(console.log)",
+            sleep=1)
+        assertEqual(out, 'Promise {}\nconsole.log("Hello World");\n\n')
+        assertEqual(err, '')
+        assertEqual(code, 0)
+
     def test_syntax_error(self):
         out, err, code = self.input("syntax error")
         assertEqual(out, '')
-        assertEqual(err, "SyntaxError: Unexpected identifier\n")
+        assert "Unexpected identifier" in err
         assertEqual(code, 0)
 
     def test_type_error(self):
         out, err, code = self.input("console()")
         assertEqual(out, '')
-        assertEqual(err, 'TypeError: console is not a function\n')
+        assert "console is not a function" in err
         assertEqual(code, 0)
 
     def test_variable(self):
@@ -126,6 +135,12 @@ class Repl(object):
         assertEqual(err, '')
         assertEqual(code, 0)
 
+    def test_lexical_scoped_variable(self):
+        out, err, code = self.input("let a = 123;", "a")
+        assertEqual(out, 'undefined\n123\n')
+        assertEqual(err, '')
+        assertEqual(code, 0)
+
 
 def assertEqual(left, right):
     if left != right: