CODEWITHSUNDEEP
javascriptarcgis
yeeen
yeeen

Reputation: 4945

Why the need for if(0) and if(1)

Look at this piece for code in ArcGIS 3.0 for javascript. https://serverapi.arcgisonline.com/jsapi/arcgis/?v=3.0

Inside there is "if(0)" and "if(1)", why is there a need for this? Isn't if(0) always false and if(1) always true?

Upvotes: 5

Views: 5957

Answers (3)

RandomActOfCoding
RandomActOfCoding

Reputation: 41

The Dojo build tools are what does that (under given build options), but not for obfuscation. If you look at non-built dojo.js and corresponding built dojo.js.uncompressed.js files, you can see that the build tool is replacing has("somefeature") calls with hardwired true/false tests. As noticed, this can and does create unreachable code. Why do this? Because then a smart optimizing compiler (e.g. Google Closure) can prune all that dead code out, resulting in a smaller file (sometimes MUCH smaller...that's the point).

Conceptually, it goes something like this:

  1. Non-built code has "kitchen sink" with dynamically-evaluated has() calls.
  2. You configure build profile with options indicating what you do/don't want in your custom build.
  3. Build process substitutes dynamic has() calls [for corresponding build options] with hardwired true/false tests (or better way to look at it is in/out tests).
  4. Closure compiler removes the "out" code during minification.

Check out current "Dojo Build System" documentation and http://jamesthom.as/blog/2012/08/03/finding-nano/ for more info. Also, here's a good low/code-level description of this process.

P.S. "if(0)/if(1)" isn't really obfuscation...kinda the opposite. If someone wanted to confuse, they'd more likely have "if(a)...if(b)...if(c)..." with vars set far, far away. However, minifiers produce more obfuscated code than that on their own. Check out dojo.js source before and after it's been run through Closure; the end product bears little resemblance to original.

Upvotes: 4

houbysoft
houbysoft

Reputation: 33412

Yes, 0 is always false and 1 is always true.

However as you can see in the code, the company considers it their trade secret:

COPYRIGHT 2009 ESRI

 TRADE SECRETS: ESRI PROPRIETARY AND CONFIDENTIAL
 Unpublished material - all rights reserved under the
 Copyright Laws of the United States and applicable international
 laws, treaties, and conventions.

It is common to obfuscate such code (i.e. making it harder to read). One of the ways is inserting useless statements like the if(1) and if(0) you have seen.

You can read more about Obfuscation here.

Another possible explanation is that these if statements are used in place of real logic that has yet to be implemented, as @mvbl fst mentioned.

Upvotes: 2

mvbl fst
mvbl fst

Reputation: 5263

This may be used in place of real if() statement for which actual logic has not been implemented yet. And as @houbysoft mentioned, they are interpreted as boolean false and true. So for the mean time they use false or true to make sure statements inside always execute (or not) and intend to add actual checks later.

Upvotes: 1

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