repl: improve .help message

- Added dots to printed commands.
- Use spaces instead of tabs so there's no misalignment on terminals
  with a tab size other than 4.
- Improved the help text for .editor and .help.
- Automatically indent command help based on the longest command.

PR-URL: nodejs#8519
Reviewed-By: Anna Henningsen <[email protected]>
Reviewed-By: James M Snell <[email protected]>
Reviewed-By: Prince John Wesley <[email protected]>
Reviewed-By: Ilkka Myller <[email protected]>

lib/repl.js

@@ -1257,12 +1257,17 @@ function defineDefaultCommands(repl) {
   });
 
   repl.defineCommand('help', {
-    help: 'Show repl options',
+    help: 'Print this help message',
     action: function() {
-      var self = this;
-      Object.keys(this.commands).sort().forEach(function(name) {
-        var cmd = self.commands[name];
-        self.outputStream.write(name + '\t' + (cmd.help || '') + '\n');
+      const names = Object.keys(this.commands).sort();
+      const longestNameLength = names.reduce((max, name) => {
+        return Math.max(max, name.length);
+      }, 0);
+      names.forEach((name) => {
+        const cmd = this.commands[name];
+        const spaces = ' '.repeat(longestNameLength - name.length + 3);
+        const line = '.' + name + (cmd.help ? spaces + cmd.help : '') + '\n';
+        this.outputStream.write(line);
       });
       this.displayPrompt();
     }
@@ -1308,7 +1313,7 @@ function defineDefaultCommands(repl) {
   });
 
   repl.defineCommand('editor', {
-    help: 'Entering editor mode (^D to finish, ^C to cancel)',
+    help: 'Enter editor mode',
     action() {
       if (!this.terminal) return;
       this.editorMode = true;

test/parallel/test-repl-definecommand.js

@@ -35,8 +35,8 @@ r.defineCommand('say2', function() {
 });
 
 inputStream.write('.help\n');
-assert(/\nsay1\thelp for say1\n/.test(output), 'help for say1 not present');
-assert(/\nsay2\t\n/.test(output), 'help for say2 not present');
+assert(/\n.say1     help for say1\n/.test(output), 'help for say1 not present');
+assert(/\n.say2\n/.test(output), 'help for say2 not present');
 inputStream.write('.say1 node developer\n');
 assert(/> hello node developer/.test(output), 'say1 outputted incorrectly');
 inputStream.write('.say2 node developer\n');