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

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!;
+}