jit.gl.Mesh how to retrieve index of face ?

Hi ,

I'have a matrix for example a dim 3*3 to generate a mesh using tri_grid as draw_mode

i keep datas in js :
-----------------------js ---------------------
for(var i = 0; i< m.dim[0]; i++){
    for(var j = 0; j< m.dim[1]; j++){
        myarray.push(m.getcell([i,j]))
    }
}
-----------------------js ---------------------

Now i want to get a new array with index of faces wich must be like :
F1 0,1,3
F2 1,3,4
F3 1,2,4
F4 2,4,5
F5 3,4,6
F6 4,6,7
F7 4,5,7
F8 5,7,8

i tried but i can't see how to process, if someone could point me on the good direction....