readline: allow passing prompt to constructor

doc/api/readline.md

@@ -357,6 +357,7 @@ added: v0.1.98
     the history set this value to `0`. Defaults to `30`. This option makes sense
     only if `terminal` is set to `true` by the user or by an internal `output`
     check, otherwise the history caching mechanism is not initialized at all.
+  * `prompt` - the prompt string to use. Default: `'> '`
 
 The `readline.createInterface()` method creates a new `readline.Interface`
 instance.
@@ -467,9 +468,12 @@ implement a small command-line interface:
 
 ```js
 const readline = require('readline');
-const rl = readline.createInterface(process.stdin, process.stdout);
+const rl = readline.createInterface({
+  input: process.stdin,
+  output: process.stdout,
+  prompt: 'OHAI> '
+});
 
-rl.setPrompt('OHAI> ');
 rl.prompt();
 
 rl.on('line', (line) => {

lib/readline.js

@@ -44,13 +44,17 @@ function Interface(input, output, completer, terminal) {
 
   EventEmitter.call(this);
   var historySize;
+  let prompt = '> ';
 
   if (arguments.length === 1) {
     // an options object was given
     output = input.output;
     completer = input.completer;
     terminal = input.terminal;
     historySize = input.historySize;
+    if (input.prompt !== undefined) {
+      prompt = input.prompt;
+    }
     input = input.input;
   }
 
@@ -87,7 +91,7 @@ function Interface(input, output, completer, terminal) {
     };
   }
 
-  this.setPrompt('> ');
+  this.setPrompt(prompt);
 
   this.terminal = !!terminal;
 

lib/repl.js

@@ -385,11 +385,10 @@ function REPLServer(prompt,
     output: self.outputStream,
     completer: complete,
     terminal: options.terminal,
-    historySize: options.historySize
+    historySize: options.historySize,
+    prompt
   });
 
-  self.setPrompt(prompt !== undefined ? prompt : '> ');
-
   this.commands = Object.create(null);
   defineDefaultCommands(this);
 
@@ -408,8 +407,6 @@ function REPLServer(prompt,
     };
   }
 
-  self.setPrompt(self._prompt);
-
   self.on('close', function() {
     self.emit('exit');
   });

test/parallel/test-readline-interface.js

@@ -1,11 +1,13 @@
 // Flags: --expose_internals
 'use strict';
-require('../common');
+const common = require('../common');
 const assert = require('assert');
 const readline = require('readline');
 const internalReadline = require('internal/readline');
 const EventEmitter = require('events').EventEmitter;
 const inherits = require('util').inherits;
+const Writable = require('stream').Writable;
+const Readable = require('stream').Readable;
 
 function FakeInput() {
   EventEmitter.call(this);
@@ -396,4 +398,29 @@ function isWarned(emitter) {
     });
   });
 
+  {
+    const expected = terminal
+      ? ['\u001b[1G', '\u001b[0J', '$ ', '\u001b[3G']
+      : ['$ '];
+
+    let counter = 0;
+    const output = new Writable({
+      write: common.mustCall((chunk, enc, cb) => {
+        assert.strictEqual(chunk.toString(), expected[counter++]);
+        cb();
+        rl.close();
+      }, expected.length)
+    });
+
+    const rl = readline.createInterface({
+      input: new Readable({ read: () => {} }),
+      output: output,
+      prompt: '$ ',
+      terminal: terminal
+    });
+
+    rl.prompt();
+
+    assert.strictEqual(rl._prompt, '$ ');
+  }
 });