readline: refactor construct Interface

Remove the dependency on the arguments.length.

PR-URL: #4740
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Trevor Norris <trev.norris@gmail.com>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>

lib/readline.js

@@ -24,22 +24,13 @@ const stripVTControlCharacters = internalReadline.stripVTControlCharacters;
 
 
 exports.createInterface = function(input, output, completer, terminal) {
-  var rl;
-  if (arguments.length === 1) {
-    rl = new Interface(input);
-  } else {
-    rl = new Interface(input, output, completer, terminal);
-  }
-  return rl;
+  return new Interface(input, output, completer, terminal);
 };
 
 
 function Interface(input, output, completer, terminal) {
   if (!(this instanceof Interface)) {
-    // call the constructor preserving original number of arguments
-    const self = Object.create(Interface.prototype);
-    Interface.apply(self, arguments);
-    return self;
+    return new Interface(input, output, completer, terminal);
   }
 
   this._sawReturnAt = 0;
@@ -51,7 +42,7 @@ function Interface(input, output, completer, terminal) {
   let crlfDelay;
   let prompt = '> ';
 
-  if (arguments.length === 1) {
+  if (input && input.input) {
     // an options object was given
     output = input.output;
     completer = input.completer;