Comments on: with Statement Considered Harmful

By: ECMAScript 5, die nächste Version von JavaScript – Teil 1: Ein Überblick • Peter Kröner, Webdesigner & Frontendentwickler

Tue, 05 Apr 2011 08:30:46 +0000

[...] von Scripts können in einen Strict Mode versetzt werden, in dem einige defekte JS-Altlasten (z.B. with(){}) nicht mehr verwendet werden können und der an einigen Stellen die Regeln von JavaScript so [...]

By: danomator

danomator — Fri, 04 Mar 2011 15:16:34 +0000

This might be a solution to the problem if anyone really needs to use with():

var obj = {a : ‘foo’, b : ‘bar’}, b = ‘brain’;

// add _ prefix to object elements
function _(obj)
{
for (var prop in obj)
this['_'+prop] = obj[prop];
}

// write obj.a and obj.b
with (obj)
{
document.write(a);
document.write(b);
}

document.write(”);

// write obj.a and global b
with (new _(obj))
{
document.write(_a);
document.write(b);
}

// original object still remains
for (var prop in obj)
document.write(”+prop+’ = ‘+obj[prop]);

By: Douglas Crockford

Douglas Crockford — Tue, 22 Feb 2011 19:59:17 +0000

The point is not that -with- is useless. The point is that it is, unfortunately, dangerous. And that it is, fortunately, unnecessary. Features that are both dangerous and unnecessary should to be used at all.

By: Why is the "with" statement in JavaScript often discouraged? - Quora

Why is the "with" statement in JavaScript often discouraged? - Quora — Thu, 17 Feb 2011 09:40:30 +0000

[...] geek, loves Mac a… To add, this article and also it's comments highlight few points. http://www.yuiblog.com/blog/2006... Another point to add, I think it also hurts performance because it adds one more level of scope [...]

By: jameshooo

jameshooo — Wed, 26 Jan 2011 06:27:36 +0000

(function(){
with(this){ // ‘this’ is one of scope chains
bing = true;
bang = true;
}
}).apply(ooo.eee.oo.ah_ah.ting.tang.walla.walla);

If ‘bing’ is member of walla, then walla.bing will be setted.
If ‘bing’ is not member of walla, then bing will be global variant.

By: Improve page load times by compressing code; or, "mnfy ur JS" | Scott Bush

Tue, 28 Dec 2010 00:52:28 +0000

[...] way only works if you avoid using the javascript function eval() and statement with, both of which are vilified for their blocking of javascript minifying, among other issues.) A real-world example of [...]

By: MooGoo

MooGoo — Tue, 14 Sep 2010 15:19:19 +0000

“You could also write that as

Math.cos(Math.asin(0.5))

which would be smaller, faster, and more legible.”

Or you could write it as

with(Math) cos(asin(0.5));

Which is even smaller, much more legible, and importantly, far more similar to what real mathematical equations look like.

I also doubt very much that this is in any significant way slower than referencing ‘Math’ multiple times.

It is probably not worth the trouble to use ‘with’ for a mere 2 function calls, but if you are doing much more, it seems like a great way to make your code more legible. And in the case of ‘with(Math)’ there is absolutely no ambiguity about what object sin/cos/floor/ceil/pow etc. come from.

By: mynamehere

mynamehere — Mon, 13 Sep 2010 22:33:53 +0000

Okay, I think we can all agree that, when talking about the ooo.eee.oo.ah_ah.ting.tang.walla.walla object, it is NEVER a good idea–due to certain nebulous security issues inherent in the JavaScript engine–to set bing AND bang to true at the same time!

By: Christian Sciberras

Christian Sciberras — Mon, 06 Sep 2010 10:13:32 +0000

By the same reasoning…

var test='global';


function doTest(){

  var test='function';

  return test;

}
alert(doTest());

alert(test);

By: Daniel Ribeiro

Daniel Ribeiro — Wed, 18 Aug 2010 02:03:44 +0000

This is all very pretty, and nice to know, and should be accepted as norm of regular code. However, DSLs are very useful, are not normal code in most languages (method chaining technique is famous for breaking Law of Demeter), as Martin Fowler says on his introduction to the topic: As you can see methods defined for Method Chaining violate basic rules for API design. A DSL (with stripped commas for a bit less of noise) that is only possible with the 'with' statement (or instance_eval in Ruby):

DSLRunner.run(function() { bake(function() { addIngredient('flour') addIngredient('yeast') addIngredient('water') print("Baking bread") }); bake(function() { print("Baking a cake") });

Remember: Rebels learn the rules better than the rule-makers do. Rebels learn where the holes are, where the rules can be breached. Become an expert at the rules. Then break them with creativity and style. -Kristine Kathryn Rusch