4 files changed, 35 insertions, 20 deletions

diff --git a/js/errors.ts b/js/errors.ts
new file mode 100644
index 000000000..2fca10eaf
--- /dev/null
+++ b/js/errors.ts
@@ -0,0 +1,15 @@
+import { deno as fbs } from "gen/msg_generated";
+
+export class DenoError<T extends fbs.ErrorKind> extends Error {
+  constructor(readonly kind: T, msg: string) {
+    super(msg);
+    this.name = `deno.${fbs.ErrorKind[kind]}`;
+  }
+}
+
+export function maybeThrowError(base: fbs.Base): void {
+  const kind = base.errorKind();
+  if (kind !== fbs.ErrorKind.NoError) {
+    throw new DenoError(kind, base.error()!);
+  }
+}
diff --git a/js/os.ts b/js/os.ts
index bd7754ea0..22ef6ef4f 100644
--- a/js/os.ts
+++ b/js/os.ts
@@ -3,6 +3,7 @@ import { ModuleInfo } from "./types";
 import { deno as fbs } from "gen/msg_generated";
 import { assert } from "./util";
 import * as util from "./util";
+import { maybeThrowError } from "./errors";
 import { flatbuffers } from "flatbuffers";
 import { libdeno } from "./globals";
 
@@ -43,9 +44,7 @@ export function codeFetch(
   // null assertion `!`
   const bb = new flatbuffers.ByteBuffer(new Uint8Array(resBuf!));
   const baseRes = fbs.Base.getRootAsBase(bb);
-  if (fbs.Any.NONE === baseRes.msgType()) {
-    throw Error(baseRes.error()!);
-  }
+  maybeThrowError(baseRes);
   assert(fbs.Any.CodeFetchRes === baseRes.msgType());
   const codeFetchRes = new fbs.CodeFetchRes();
   assert(baseRes.msg(codeFetchRes) != null);
@@ -82,10 +81,7 @@ export function codeCache(
   if (resBuf != null) {
     const bb = new flatbuffers.ByteBuffer(new Uint8Array(resBuf));
     const baseRes = fbs.Base.getRootAsBase(bb);
-    assert(fbs.Any.NONE === baseRes.msgType());
-    // undefined and null are incompatible in strict mode, but at runtime
-    // a null value is fine, therefore not null assertion
-    throw Error(baseRes.error()!);
+    maybeThrowError(baseRes);
   }
 }
 
@@ -112,11 +108,7 @@ export function readFileSync(filename: string): Uint8Array {
   // null assertion `!`
   const bb = new flatbuffers.ByteBuffer(new Uint8Array(resBuf!));
   const baseRes = fbs.Base.getRootAsBase(bb);
-  if (fbs.Any.NONE === baseRes.msgType()) {
-    // undefined and null are incompatible in strict mode, but at runtime
-    // a null value is fine, therefore not null assertion
-    throw Error(baseRes.error()!);
-  }
+  maybeThrowError(baseRes);
   assert(fbs.Any.ReadFileSyncRes === baseRes.msgType());
   const res = new fbs.ReadFileSyncRes();
   assert(baseRes.msg(res) != null);
diff --git a/js/runtime.ts b/js/runtime.ts
index 1a9e8497d..93649e11c 100644
--- a/js/runtime.ts
+++ b/js/runtime.ts
@@ -176,14 +176,7 @@ export function resolveModule(
   } else {
     // We query Rust with a CodeFetch message. It will load the sourceCode, and
     // if there is any outputCode cached, will return that as well.
-    let fetchResponse;
-    try {
-      fetchResponse = os.codeFetch(moduleSpecifier, containingFile);
-    } catch (e) {
-      // TODO Only catch "no such file or directory" errors. Need error codes.
-      util.log("os.codeFetch error ignored", e.message);
-      return null;
-    }
+    const fetchResponse = os.codeFetch(moduleSpecifier, containingFile);
     filename = fetchResponse.filename;
     sourceCode = fetchResponse.sourceCode;
     outputCode = fetchResponse.outputCode;
diff --git a/js/unit_tests.ts b/js/unit_tests.ts
index 96341b4a2..ef65519f6 100644
--- a/js/unit_tests.ts
+++ b/js/unit_tests.ts
@@ -92,6 +92,21 @@ test(async function tests_readFileSync() {
   assertEqual(pkg.name, "deno");
 });
 
+/* TODO We should be able to catch specific types.
+test(function tests_readFileSync_NotFound() {
+  let caughtError = false;
+  let data;
+  try {
+    data = readFileSync("bad_filename");
+  } catch (e) {
+    caughtError = true;
+    assert(e instanceof deno.NotFound);
+  }
+  assert(caughtError);
+  assert(data === undefined);
+});
+*/
+
 test(async function tests_fetch() {
   const response = await fetch("http://localhost:4545/package.json");
   const json = await response.json();