console: refactor the console module to be reusable

So that multiple instances can be created pointing
to different writable streams.

This is needed for #3876.

lib/console.js

@@ -21,57 +21,88 @@
 
 var util = require('util');
 
-exports.log = function() {
-  process.stdout.write(util.format.apply(this, arguments) + '\n');
+function Console(stdout, stderr) {
+  if (!(this instanceof Console)) {
+    return new Console(stdout, stderr);
+  }
+  if (!stdout || typeof stdout.write !== 'function') {
+    throw new TypeError('Console expects a writable stream instance');
+  }
+  if (!stderr) {
+    stderr = stdout;
+  }
+  var prop = {
+    writable: true,
+    enumerable: false,
+    configurable: true
+  };
+  prop.value = stdout;
+  Object.defineProperty(this, '_stdout', prop);
+  prop.value = stderr;
+  Object.defineProperty(this, '_stderr', prop);
+  prop.value = {};
+  Object.defineProperty(this, '_times', prop);
+
+  // bind the prototype functions to this Console instance
+  Object.keys(Console.prototype).forEach(function(k) {
+    this[k] = this[k].bind(this);
+  }, this);
+}
+
+Console.prototype.log = function() {
+  this._stdout.write(util.format.apply(this, arguments) + '\n');
 };
 
 
-exports.info = exports.log;
+Console.prototype.info = Console.prototype.log;
 
 
-exports.warn = function() {
-  process.stderr.write(util.format.apply(this, arguments) + '\n');
+Console.prototype.warn = function() {
+  this._stderr.write(util.format.apply(this, arguments) + '\n');
 };
 
 
-exports.error = exports.warn;
+Console.prototype.error = Console.prototype.warn;
 
 
-exports.dir = function(object) {
-  process.stdout.write(util.inspect(object) + '\n');
+Console.prototype.dir = function(object) {
+  this._stdout.write(util.inspect(object) + '\n');
 };
 
 
-var times = {};
-exports.time = function(label) {
-  times[label] = Date.now();
+Console.prototype.time = function(label) {
+  this._times[label] = Date.now();
 };
 
 
-exports.timeEnd = function(label) {
-  var time = times[label];
+Console.prototype.timeEnd = function(label) {
+  var time = this._times[label];
   if (!time) {
     throw new Error('No such label: ' + label);
   }
   var duration = Date.now() - time;
-  exports.log('%s: %dms', label, duration);
+  this.log('%s: %dms', label, duration);
 };
 
 
-exports.trace = function(label) {
+Console.prototype.trace = function(label) {
   // TODO probably can to do this better with V8's debug object once that is
   // exposed.
   var err = new Error;
   err.name = 'Trace';
   err.message = label || '';
   Error.captureStackTrace(err, arguments.callee);
-  console.error(err.stack);
+  this.error(err.stack);
 };
 
 
-exports.assert = function(expression) {
+Console.prototype.assert = function(expression) {
   if (!expression) {
     var arr = Array.prototype.slice.call(arguments, 1);
     require('assert').ok(false, util.format.apply(this, arr));
   }
 };
+
+
+module.exports = new Console(process.stdout, process.stderr);
+module.exports.Console = Console;

test/simple/test-console-instance.js

@@ -0,0 +1,80 @@
+// Copyright Joyent, Inc. and other Node contributors.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a
+// copy of this software and associated documentation files (the
+// "Software"), to deal in the Software without restriction, including
+// without limitation the rights to use, copy, modify, merge, publish,
+// distribute, sublicense, and/or sell copies of the Software, and to permit
+// persons to whom the Software is furnished to do so, subject to the
+// following conditions:
+//
+// The above copyright notice and this permission notice shall be included
+// in all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
+// OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN
+// NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
+// DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
+// OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE
+// USE OR OTHER DEALINGS IN THE SOFTWARE.
+
+
+var common = require('../common');
+var assert = require('assert');
+var Stream = require('stream');
+var Console = require('console').Console;
+var called = false;
+
+// ensure the Console instance doesn't write to the
+// process' "stdout" or "stderr" streams
+process.stdout.write = process.stderr.write = function() {
+  throw new Error('write() should not be called!');
+};
+
+// make sure that the "Console" function exists
+assert.equal('function', typeof Console);
+
+// make sure that the Console constructor throws
+// when not given a writable stream instance
+assert.throws(function () {
+  new Console();
+}, /Console expects a writable stream/);
+
+var out = new Stream();
+var err = new Stream();
+out.writable = err.writable = true;
+out.write = err.write = function(d) {};
+
+var c = new Console(out, err);
+
+out.write = err.write = function(d) {
+  assert.equal(d, 'test\n');
+  called = true;
+};
+
+assert(!called);
+c.log('test');
+assert(called);
+
+called = false;
+c.error('test');
+assert(called);
+
+out.write = function(d) {
+  assert.equal('{ foo: 1 }\n', d);
+  called = true;
+};
+
+called = false;
+c.dir({ foo: 1 });
+assert(called);
+
+// ensure that the console functions are bound to the console instance
+called = 0;
+out.write = function(d) {
+  called++;
+  assert.equal(d, called + ' ' + (called - 1) + ' [ 1, 2, 3 ]\n');
+};
+[1, 2, 3].forEach(c.log);
+assert.equal(3, called);