nodejs setInterval and setTimeout doesn't persist scope

timerScopeIssue.coffee

#!/usr/bin/coffee

###
 node v0.8.15
###

# this doesn't work for setInterval either
class Test

  constructor: (@text) ->

  delay: 2000

  print: -> console.log @text

  shouldWork: -> setTimeout @print, @delay

  shouldWorkClosure: ->
    obj = @ # closure
    setTimeout obj.print, @delay

  workingClosure: ->
    obj = @ # closure
    func = ->
      obj.print()
    setTimeout func, @delay

test = new Test 'dummy text'
test.print() # prints text
test.shouldWork() # undefined
test.shouldWorkClosure() # undefined
test.workingClosure() # prints text

timerScopeIssue.js

// Generated by CoffeeScript 1.4.0
/*
 node v0.8.15
*/

var Test, test;

Test = (function() {

  function Test(text) {
    this.text = text;
  }

  Test.prototype.delay = 2000;

  Test.prototype.print = function() {
    return console.log(this.text);
  };

  Test.prototype.shouldWork = function() {
    return setTimeout(this.print, this.delay);
  };

  Test.prototype.shouldWorkClosure = function() {
    var obj;
    obj = this;
    return setTimeout(obj.print, this.delay);
  };

  Test.prototype.workingClosure = function() {
    var func, obj;
    obj = this;
    func = function() {
      return obj.print();
    };
    return setTimeout(func, this.delay);
  };

  return Test;

})();

test = new Test('dummy text');

test.print();

test.shouldWork();

test.shouldWorkClosure();

test.workingClosure();

Let me introduce you to my little friend Function.prototype.bind.

   Test.prototype.shouldWork = function() {
-    return setTimeout(this.print, this.delay);
+    return setTimeout(this.print.bind(this), this.delay);
   };

   Test.prototype.shouldWorkClosure = function() {
      var obj;
      obj = this;
-    return setTimeout(obj.print, this.delay);
+    return setTimeout(obj.print.bind(this), this.delay);
   };

This is a general question about the value of this in JavaScript. Has nothing to do with Node or setTimeout in particular.

I was expecting 'this' would be function I am passing to setTimeout - but it isn't. Still I have learned new thing today - so thank you Isaac for your response. :)

Ok, so it is really known issue :-/ https://developer.mozilla.org/en-US/docs/JavaScript/Reference/Global_Objects/Function/bind