Port Expander (working module code inside - how does it look)

I just tried this out on an MCP23008... it actually seems to work

exports.connect = function(i2c,rst,i2ca) {
	
    return new MCP32x08(i2c,rst,i2ca);
};

function MCP32x08(i2c,rst, i2ca) {
  rst.write(0);
  this.i2c = i2c;
  this.i2ca = (i2ca===undefined) ? 32:32+i2ca;
  this.rst=rst;
  this.m=255;
  this.pu=0;
  this.olat=0;
  this.rst.write(1);
  this.A0=new PEP(0,this);
  this.A1=new PEP(1,this);
  this.A2=new PEP(2,this);
  this.A3=new PEP(3,this);
  this.A4=new PEP(4,this);
  this.A5=new PEP(5,this);
  this.A6=new PEP(6,this);
  this.A7=new PEP(7,this);
}

MCP32x08.prototype.s=function(r,d){this.­i2c.writeTo(this.i2ca,r,d);};
MCP32x08.prototype.r=function(r){this.i2­c.writeTo(this.i2ca,r);return this.i2c.readFrom(this.i2ca,1)};

MCP32x08.prototype.mode=function(pin,mod­e) {
	var bv=1<<pin;
	this.s(0,mode=='output'?(this.m&=~bv):(t­his.m |=bv));
	this.s(6,mode=='input_pullup'?(this.pu|=­bv):(this.pu&=~bv));
};
MCP32x08.prototype.write=function(pin,va­l) {
	var bv=1<<pin;
	this.olat&=~bv;
	this.s(9,this.olat|=(bv*val));
}; 
MCP32x08.prototype.read=function(pin) {
	var bv=1<<pin;
	return (this.r(9)[0]&bv)>>pin;
}; 

function PEP (b,p){
	this.b=b;
	this.p=p;
}
PEP.prototype.set=function(){this.p.writ­e(this.b,1)};
PEP.prototype.unset=function(){this.p.wr­ite(this.b,0)};
PEP.prototype.write=function(v){this.p.w­rite(this.b,v)};
PEP.prototype.read=function(){return this.p.read(this.b)};
PEP.prototype.mode=function(m){this.p.mo­de(this.b,m)};

>process.memory();
={ "free": 4824, "usage": 276, "total": 5100, "history": 121,
  "stackEndAddress": 536958396, "flash_start": 134217728, "flash_binary_end": 317952, "flash_code_start": 134234112, "flash_length": 393216 }
>pe.A4.mode('input_pullup');
=undefined
>pe.A4.read()
=1
>pe.A4.mode('output');
=undefined
>pe.A4.read();
=0
>pe.A4.set()
=undefined
>pe.A4.read();
=1
>pe.A4.unset();
=undefined
>pe.A4.read();
=0
> 

much easier than I'd expected (though there's still some more to to, including expanding to the 16-bit version (there are two ways the data can be organized...)