Tricky inheritance issue with FF 29 #195

jambonnade · 2014-05-06T14:04:22Z

Hi,

We have a bug that appeared with Firefox 29 : some property in one object is lost when calling a redefined method.
The conditions to reproduce are very particular but I identified them. Maybe it may lead to identify a bigger problem.

Here is the code

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="fr" lang="fr">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
    <title>Title</title>
    <script src="http://ajax.googleapis.com/ajax/libs/prototype/1.7.2.0/prototype.js"></script>
</head>
<body>
    <div><textarea id="log" rows="10" cols="80"></textarea></div>
    <p><button type="button" id="btn">demo</button></p>
    <script type="text/javascript">/* <!-- */

        var SuperClass = Class.create({
            'initialize': function () {
                this.data1 = 'a';
                this.data2 = 'b';

                // My "fix" is to make the browser fetch the properties with
                // this, it seems the bug doesn't appear then
                //Object.keys(this);

                this.log('init');
                //this.log('data3 (0) : "' + this.data3 + '"');

                // meth1 adds data3 in SubClassA
                this.meth1();
                this.log('data3 (1) : "' + this.data3 + '"');

                // meth2 erases data3 in SubClassA (bug)
                this.meth2();
                this.log('data3 (2) : "' + this.data3 + '"');

                this.log('\n');
            },

            'meth1': function () {
                this.log('meth1');
            },
            'meth2': function () {
                this.log('meth2');
                // meth2 needs to add data in SuperClass to trigger the bug
                this.data4 = 'x';
            },
            'log': function (stuff) {
                $('log').value += stuff + "\n";
            }
        });

        var SubClassA = Class.create(SuperClass, {
            'meth1': function () {
                this.log('meth1 (sub)');
                this.data3 = 'z';
            },
            'meth2': function ($super) {
                // meth2 needs to be redefined to trigger the bug
                this.log('meth2 (sub with super())');
                $super();
            }
        });

        var SubClassB = Class.create(SuperClass, {
            // Whatever here
        });


        $('btn').observe('click', function () {
            // Need to init another object from another subclass to trigger
            // the bug.
            new SubClassB();
            // Bugged object :
            new SubClassA();
        });

    /* --> */</script>
</body>
</html>

jambonnade · 2014-05-06T14:31:21Z

I forgot to mention : doesn't happen if firebug (or dev console) is opened. I believe firebug accesses the created objects in some way ; that's why, i added "Object.keys()" to fix, it may do the same kind of stuff internally.

Yaffle · 2014-05-06T15:46:20Z

@Gruikmusic , interesting bug, did you post a report at bugzilla.mozilla.org ?
i can reproduce this without prototype.js :

<script>
function SuperClass() {
  this.meth1();
  var z = this.data3;
  this.meth2();
  if (z !== this.data3) {
    alert('bug!');
  }
}
SuperClass.prototype.meth1 = function () {
};
SuperClass.prototype.meth2 = function () {
  this.data4 = 'x';
};
var F = function () {
};
F.prototype = SuperClass.prototype;
function SubClassA() {
  SuperClass.call(this);
}
SubClassA.prototype = new F();
SubClassA.prototype.meth1 = function () {
  this.data3 = 'z';
};
SubClassA.prototype.meth2 = function () {
};
function SubClassB() {
  SuperClass.call(this);
}
SubClassB.prototype = new F();
new SubClassB();
new SubClassA();
</script>

jambonnade · 2014-05-06T15:52:36Z

i prefered to let you (prototypejs contributors) report to mozilla when found whether it's related to firefox or prototypejs

Yaffle · 2014-05-07T09:05:59Z

@Gruikmusic , so you have to wait prototypejs contributors to do this....
Anyway, i think, it is not good, that common constructor creates different properties on an object, because of redefined "meth1" and "meth2"...

jambonnade · 2014-05-09T18:54:45Z

I reported to mozilla https://bugzilla.mozilla.org/show_bug.cgi?id=1008339

About derived methods in constructor, I'm used to do this in PHP and I find it interesting :

class Parent
{
  public function __construct($params)
  {
     // [...]

     $this->_initSomeStuff();
     $this->_initOtherStuff();

     // [...]
  }
  protected function _initSomeStuff()
  {
    // default code
  }
  protected function _initOtherStuff()
  {
    // default code
  }
}

_initSomeStuff and _initOtherStuff may be overridden then in subclasses to customize some parts of initialization while keeping a common construction (and a common constructor signature)

Yaffle · 2014-05-09T19:19:52Z

I reported to mozilla https://bugzilla.mozilla.org/show_bug.cgi?id=1008339

good.
;

About derived methods in constructor, I'm used to do this in PHP and I find it interesting :
Thats OK.

But in javascript the sequence of property assignments affects the "class" of an object.
So, it is better to define all properties in the constructor.

savetheclocktower · 2015-05-13T03:48:09Z

Looks like Firefox fixed this, which is good, because I wouldn't have known where to start. Thanks!

savetheclocktower closed this as completed May 13, 2015

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Tricky inheritance issue with FF 29 #195

Tricky inheritance issue with FF 29 #195

jambonnade commented May 6, 2014

jambonnade commented May 6, 2014

Yaffle commented May 6, 2014

jambonnade commented May 6, 2014

Yaffle commented May 7, 2014

jambonnade commented May 9, 2014

Yaffle commented May 9, 2014

savetheclocktower commented May 13, 2015

Tricky inheritance issue with FF 29 #195

Tricky inheritance issue with FF 29 #195

Comments

jambonnade commented May 6, 2014

jambonnade commented May 6, 2014

Yaffle commented May 6, 2014

jambonnade commented May 6, 2014

Yaffle commented May 7, 2014

jambonnade commented May 9, 2014

Yaffle commented May 9, 2014

savetheclocktower commented May 13, 2015