small preprocessor - #ifdef like statement ?

[espruino-discuss]

Posted at 2014-03-17 by Sacha

Hi Gordon,

It would be very nice if a tiny preprocessor with #ifdef / #endif statements where included in WebIDE. I would like to strip out debug code that way.

Regards

Sacha

[gfwilliams]

Posted at 2014-03-17 by @gfwilliams

Hmm, it's a thought. I wonder whether minification could be modified to do what you want though. For instance:

var DBG = false;

if (DBG) console.log("Debug");
console.log("Foo");

That actually works fine when minified - it goes down to:

var DBG=!1;console.log("Foo");

However when in a function, it doesn't work properly (because it thinks that the state of DBG might get changed). Object.freeze doesn't seem to work either. You could do:

(function() {
  var DBG = false;

  function foo() {
    if (DBG) console.log("Debug");
    console.log("Foo");
  }

  setTimeout(foo,1000);
})();

And that minifies down really nicely:

(function(){setTimeout(function(){console.log("Foo")},1E3)})();

[espruino-discuss]

Posted at 2014-03-17 by Sacha

Hello Gordon,

Adding such a feature to the minifcation would be great.

Regards

Sacha

[espruino-discuss]

Posted at 2014-03-26 by rwaldron

There are several new syntax proposals for ES7 that would like to make use of "#", as it's one of the last ascii characters available. I strongly recommend avoiding the introduction of non-standard syntactic forms.

[gfwilliams]

Posted at 2014-03-26 by @gfwilliams

@rwaldron: any thoughts on telling the minifier that DBG is a constant that doesn't change? It sounded like DBG=Object.freeze(DBG) might do it, but it didn't seem to work in the closure compiler.

[espruino-discuss]

Posted at 2014-03-26 by rwaldron

Right, that won't work—Object.freeze only sets the meta object descriptor properties to: [[configurable]]: false, [[writable]]: false. It won't turn a non-object into a const. What you could do is provide a "built-in" keyword whose value is true and is essentially a const binding. Special keywords are safe additions, as long as they're not any of the FutureReservedWords: class, enum, extends, super, const, export, import, implements, let, private, public, interface, package, protected, static or yield; additionally, there is precedent in node with bindings like process, which aren't const, but are special (if you attempt to reassign it, the process itself will crash)

[gfwilliams]

Posted at 2014-03-26 by @gfwilliams

I'm not talking about extending Espruino at all here... I can want a way to tell someone else's minifier that a value isn't going to change.

I guess I could pre-parse the code, detect the pattern var DBG = true/false; at the beginning, and then search/replace DBG with the actual value before passing the code to the minifier. It's pretty ugly though.

[espruino-discuss]

Posted at 2014-03-26 by rwaldron

I see, I misunderstood.