repl: add friendly tips about how to exit repl

Imitate python repl, when the user enters 'exit' or 'quit',
no longer prompt 'Reference Error', but
prompts 'To exit, press ^D or type .exit'.
If the user defines variables named 'exit' or 'quit' ,
only the value of the variables are output

PR-URL: #20617
Fixes: #19021
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>

lib/repl.js

@@ -215,9 +215,15 @@ function REPLServer(prompt,
 
   function defaultEval(code, context, file, cb) {
     var err, result, script, wrappedErr;
+    var isExitCommand = false;
     var wrappedCmd = false;
     var awaitPromise = false;
     var input = code;
+    var trimmedCommand = code.trim();
+
+    if (trimmedCommand === 'exit' || trimmedCommand === 'quit') {
+      isExitCommand = true;
+    }
 
     if (/^\s*\{/.test(code) && /\}\s*$/.test(code)) {
       // It's confusing for `{ a : 1 }` to be interpreted as a block
@@ -313,10 +319,16 @@ function REPLServer(prompt,
             breakOnSigint: self.breakEvalOnSigint
           };
 
+          const localContext = self.useGlobal ? global : self.context;
+          if (isExitCommand && !localContext.hasOwnProperty(trimmedCommand)) {
+            self.outputStream.write('(To exit, press ^D or type .exit)\n');
+            return self.displayPrompt();
+          }
+
           if (self.useGlobal) {
             result = script.runInThisContext(scriptOptions);
           } else {
-            result = script.runInContext(context, scriptOptions);
+            result = script.runInContext(localContext, scriptOptions);
           }
         } finally {
           if (self.breakEvalOnSigint) {
@@ -332,12 +344,10 @@ function REPLServer(prompt,
         }
       } catch (e) {
         err = e;
-
         if (err && err.code === 'ERR_SCRIPT_EXECUTION_INTERRUPTED') {
-          // The stack trace for this case is not very useful anyway.
+        // The stack trace for this case is not very useful anyway.
           Object.defineProperty(err, 'stack', { value: '' });
         }
-
         if (process.domain) {
           debug('not recoverable, send to domain');
           process.domain.emit('error', err);

test/parallel/test-repl.js

@@ -132,6 +132,29 @@ const strictModeTests = [
   }
 ];
 
+const friendlyExitTests = [
+  {
+    send: 'exit',
+    expect: '(To exit, press ^D or type .exit)'
+  },
+  {
+    send: 'quit',
+    expect: '(To exit, press ^D or type .exit)'
+  },
+  {
+    send: 'quit = 1',
+    expect: '1'
+  },
+  {
+    send: 'quit',
+    expect: '1'
+  },
+  {
+    send: 'exit',
+    expect: '(To exit, press ^D or type .exit)'
+  },
+];
+
 const errorTests = [
   // Uncaught error throws and prints out
   {
@@ -742,6 +765,7 @@ const tcpTests = [
     const [ socket, replServer ] = await startUnixRepl();
 
     await runReplTests(socket, prompt_unix, unixTests);
+    await runReplTests(socket, prompt_unix, friendlyExitTests);
     await runReplTests(socket, prompt_unix, errorTests);
     replServer.replMode = repl.REPL_MODE_STRICT;
     await runReplTests(socket, prompt_unix, strictModeTests);