add notImplemented and unreachable util functions (#540)

js/fetch.ts

@@ -4,7 +4,8 @@ import {
   log,
   createResolvable,
   Resolvable,
-  typedArrayToArrayBuffer
+  typedArrayToArrayBuffer,
+  notImplemented,
 } from "./util";
 import { pubInternal, sub } from "./dispatch";
 import { deno as pb } from "./msg.pb";
@@ -46,11 +47,11 @@ class FetchResponse implements Response {
   }
 
   blob(): Promise<Blob> {
-    throw Error("not implemented");
+    notImplemented();
   }
 
   formData(): Promise<FormData> {
-    throw Error("not implemented");
+    notImplemented();
   }
 
   async json(): Promise<object> {
@@ -69,7 +70,7 @@ class FetchResponse implements Response {
   }
 
   clone(): Response {
-    throw Error("not implemented");
+    notImplemented();
   }
 
   onHeader: (res: Response) => void;

js/os.ts

@@ -16,7 +16,7 @@ export function exit(exitCode = 0): never {
   fbs.Base.addMsgType(builder, fbs.Any.Exit);
   builder.finish(fbs.Base.endBase(builder));
   libdeno.send(builder.asUint8Array());
-  throw Error("Unreachable");
+  return util.unreachable();
 }
 
 export function codeFetch(
@@ -131,7 +131,7 @@ export function writeFileSync(
   data: Uint8Array,
   perm: number
 ): void {
-  assert(false, "Not Implemented");
+  util.notImplemented();
   /*
   pubInternal("os", {
     command: fbs.Command.WRITE_FILE_SYNC,

js/runtime.ts

@@ -313,7 +313,7 @@ class TypeScriptHost implements ts.LanguageServiceHost {
 
   readFile(path: string, encoding?: string): string | undefined {
     util.log("readFile", path);
-    throw Error("not implemented");
+    return util.notImplemented();
   }
 
   getNewLine() {

js/util.ts

@@ -67,3 +67,11 @@ export function createResolvable<T>(): Resolvable<T> {
   // therefore use of not null assertion (`!`)
   return Object.assign(promise, methods!) as Resolvable<T>;
 }
+
+export function notImplemented(): never {
+  throw new Error("Not implemented");
+}
+
+export function unreachable(): never {
+  throw new Error("Code not reachable");
+}