Fixed with 426ac06

But actually just s = SPI() will give you an object, but it won't be a proper instance of SPI. new is the thing that creates an actual usable object: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/new

The memory bug looks fixed but software SPI is not working for me. Looks like SPI() and new SPI() does the same wrong thing now.

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>var s=new SPI()
={  }
>var s=SPI()
={  }
>for(var i=0;i<2000;i++)s=new SPI();process.memory().free
=2565
> 
>var fc=new SPI();fc.setup({sck:D29,miso:D31,mosi:D30,mode:0});
Uncaught Error: Function "setup" not found!
 at line 1 col 21
var fc=new SPI();fc.setup({sck:D29,miso:D31,mosi:D30,mode:0}...
                    ^
>fc
={  }

Oops - thanks! Should have tested that :) Just fixed properly :)

It works, bug is fixed.

And now even s=SPI() and s=new SPI() seems to do same right thing. I hope I understand new keyword better now, however the confusion what is better to call x=new Date() or x=Date() is still there.

from https://stackoverflow.com/a/383503 it looks like without new the constructor is called as normal function with 'this' pointing elsewhere. And there is proposed way to 'fix' it in constructor method so it doesn't matter whether new is used or not

function foo()
{
   // if user accidentally omits the new keyword, this will 
   // silently correct the problem...
   if ( !(this instanceof foo) )
      return new foo();

And with the fix the s=SPI() works and I can't see any difference between resulting created objects with or without new.
So i guess new is better/safer/proper way but it can work without it too. Confusing :-)