More Journal of Object Technology

Journal of Object Technology

list from two years ago

• Programming with Models - Modeling with Code, The Role of Models in Software Development
• ClassSheets - model-based, object-oriented design of spreadsheet applications
• The Message-Oriented Mobility Model
• Programming the World in a Browser, Real Men Don't Do JavaScript Do They? !
• A change propagating model transformation language
• Concepts and Concept-Oriented Programming
• An enhanced form of dynamic untyped object-based inheritance
• Overview of the Panda Programming System
• Enabling Application Agility - Software as A Service, Cloud Computing and Dynamic Languages

Javascript 'with' Statement *NOT* Considered Harmful

considers the ‘with’ statement harmful

His reasoning is that if you do something like this:

with (ooo.eee.oo.ah_ah.ting.tang.walla.walla) {
    bing = true;
    bang = true;
}

Then “there is no way that you can tell by looking at the code which bing and bang will get modified”.

He instead suggests doing something like this:

var o = ooo.eee.oo.ah_ah.ting.tang.walla.walla;
o.bing = true;
o.bang = true;

But this doesn’t limit the scope of the ‘o’ variable and doesn’t have a satisfying block-structure (well, if that’s the sort of thing that brings you satisfaction).

You might think that you could do something like this:

{
   var o = ooo.eee.oo.ah_ah.ting.tang.walla.walla;
   o.bing = true;
   o.bang = true;
}
// ‘o’ is still defined here

, to limit the scope and introduce a block-structure. But in the Firefox JS implementation at least, this doesn’t actually do what you would expect. The ‘o’ variable is still defined after the end of the block.

So here’s my solution:

with ({o:ooo.eee.oo.ah_ah.ting.tang.walla.walla}) {
    o.bing = true;
    o.bang = true;
}

Or if you’re feeling a little more Smalltalk-ish:

with ({self:ooo.eee.oo.ah_ah.ting.tang.walla.walla}) {
    self.bing = true;
    self.bang = true;
}

Notice that rather than using the object directly, I've put it into a map so that I can give it an explicit name.

You can also use the same trick to define multiple variables; essentially using ‘with’ like you would use Lisp or Scheme’s ‘let’ statement.

with ({
   walla : ooo.eee.oo.ah_ah.ting.tang.walla.walla,
   wanka : ooo.eee.oo.ah_ah.ting.tank.walla.wanka
     })
{
    walla.bing = true;
    wanka.bang = true;
}

You’ve gotta love JS’s Object/Map duality.

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