more tests, fix check for completer being a function or undefined

lib/readline.js

@@ -12,7 +12,6 @@ const util = require('util');
 const inherits = util.inherits;
 const EventEmitter = require('events').EventEmitter;
 
-
 exports.createInterface = function(input, output, completer, terminal) {
   var rl;
   if (arguments.length === 1) {
@@ -49,7 +48,7 @@ function Interface(input, output, completer, terminal) {
 
   completer = completer || undefined;
 
-  if (! typeof completer in ['function', 'undefined']) {
+  if (typeof completer !== 'function' && typeof completer !== 'undefined') {
     throw new TypeError('Argument \'completer\' must be a function');
   }
 

test/parallel/test-readline-interface.js

@@ -190,6 +190,41 @@ function isWarned(emitter) {
   assert.equal(callCount, expectedLines.length);
   rli.close();
 
+  // \t does not become part of the input when there is a completer function
+  fi = new FakeInput();
+  var completer = function(line) {
+    return [[], line];
+  };
+  rli = new readline.Interface({
+    input: fi,
+    output: fi,
+    terminal: true,
+    completer: completer
+  });
+  expectedLines = ['foo'];
+  callCount = 0;
+  rli.on('line', function(line) {
+    assert.equal(line, expectedLines[callCount]);
+    callCount++;
+  });
+  fi.emit('data', '\tfo\to\t');
+  fi.emit('data', '\n');
+  assert.equal(callCount, expectedLines.length);
+  rli.close();
+
+  // constructor throws if completer is not a function or undefined
+  fi = new FakeInput();
+  assert.throws(function () {
+    readline.createInterface({
+      input: fi,
+      completer: 'string is not valid'
+    });
+  }, function (err) {
+    if ( (err instanceof TypeError) && /Argument \'completer\' must be a function/.test(err) ) {
+        return true;
+    }
+  });
+
   // sending a multi-byte utf8 char over multiple writes
   var buf = Buffer('☮', 'utf8');
   fi = new FakeInput();