Translating gl texture slab chain to Javascript

I have a simple patch which Is overlaying 2 (possibly more) gl texture layers. Im trying to translate this into Javascript but Im not getting any output. Im guessing there is an issue with one of the inputs and outputs in the chain. Ive tried a number of combinations but I'm getting nothing out. (Note: I haven't implemented the second input texture yet Im just trying to get something working for the first texture)
Any pointers to where Im going wrong gratefully received!

This is the JS:

var mycursor = new JitterObject("jit.gl.gridshape", "editor");
mycursor.shape = "plane";
mycursor.smooth_shading = 1;
mycursor.lightning_enable = 1;
scalex = 0.1;
scaley = 0.1;
mycursor.scale = [scalex,scaley];
mycursor.position = [0.2,0.2];
mycursor.color = [1,0,0,0.5];
mycursor.capture = "cursor";

var cursorsel = new JitterObject("jit.gl.texture", "editor");
cursorsel.name = "cursor";
cursorsel.dim = [320, 240];

var backdrop = new JitterObject("jit.gl.texture", "editor");
backdrop.name = "backdrop";
backdrop.dim = [320, 240];

var mixer = new JitterObject("jit.gl.slab", "editor");
mixer.inputs = 4;
mixer.file = "43j-fourwaymix.jxs";
mixer.activeinput = 0;
//mixer.texture = ["cursor", "backdrop"];
mixer.jit_gl_texture("cursor");
mixer.param = 0.9;

var displaycombined = new JitterObject("jit.gl.videoplane", "editor");
displaycombined.blend_enable = 1;
displaycombined.transform_reset = 2;
displaycombined.jit_gl_texture(mixer.out_name);

function bang ()
{
cursorsel.draw();
myrender.erase();
myrender.drawclients();
myrender.swap();
}

This is the patch its based on:
[ mod - removed uncompressed patch ]