Add repl functions "help" and "exit" (#1563)

js/repl.ts

@@ -10,6 +10,24 @@ import { globalEval } from "./global_eval";
 
 const window = globalEval("this");
 
+const helpMsg = [
+  "exit    Exit the REPL",
+  "help    Print this help message"
+].join("\n");
+
+const replCommands = {
+  exit: {
+    get() {
+      exit(0);
+    }
+  },
+  help: {
+    get() {
+      return helpMsg;
+    }
+  }
+};
+
 function startRepl(historyFile: string): number {
   const builder = flatbuffers.createBuilder();
   const historyFile_ = builder.createString(historyFile);
@@ -54,6 +72,7 @@ export async function readline(rid: number, prompt: string): Promise<string> {
 // @internal
 export async function replLoop(): Promise<void> {
   window.deno = deno; // FIXME use a new scope (rather than window).
+  Object.defineProperties(window, replCommands);
 
   const historyFile = "deno_history.txt";
   const rid = startRepl(historyFile);
@@ -69,11 +88,6 @@ export async function replLoop(): Promise<void> {
       console.error(err);
       exit(1);
     }
-    if (!code) {
-      continue;
-    } else if (code.trim() === ".exit") {
-      break;
-    }
 
     evaluate(code);
   }

tools/repl_test.py

@@ -56,11 +56,22 @@ class Repl(object):
         assertEqual(code, 0)
 
     def test_exit_command(self):
-        out, err, code = self.input(".exit", "'ignored'", exit=False)
+        out, err, code = self.input("exit", "'ignored'", exit=False)
         assertEqual(out, '')
         assertEqual(err, '')
         assertEqual(code, 0)
 
+    def test_help_command(self):
+        out, err, code = self.input("help")
+        expectedOut = '\n'.join([
+            "exit    Exit the REPL",
+            "help    Print this help message",
+            "",
+        ])
+        assertEqual(out, expectedOut)
+        assertEqual(err, '')
+        assertEqual(code, 0)
+
     def test_function(self):
         out, err, code = self.input("deno.writeFileSync")
         assertEqual(out, '[Function: writeFileSync]\n')