Passing / packing attributes to web gl shader - webgl

Question

I need help understanding how to pass an additional attribute in an existing system. I am using
nexus to render my mesh. Nexus sort of uses three.js, but down the line it actually does straight calls to web gl. I want to add a cool looking wireframe effect to it and i found this guy wireframe shader. Long story short, i added a barycentric attribute to the my shader that nexus loads. I can get the location of the attribute and all that jazz. What i am having trouble with is understanding how to modify nexus webgl calls to pass in additional data for that attribute. Code in question is this:
function readyNode(node) {
var m = node.mesh;
var n = node.id;
var nv = m.nvertices[n];
var nf = m.nfaces[n];
var model = node.model;
var vertices;
var indices;
indices = new Uint8Array(node.buffer, nv*m.vsize, nf*m.fsize);
const konSize = nv * m.vsize + 12 * nv;
vertices = new Uint8Array(konSize);
var view = new Uint8Array(node.buffer, 0, nv * m.vsize);
var v = view.subarray(0, nv*12);
vertices.set(v);
var konOff = nv*12;
var off = nv*12;
//var barycentric = addBarycentricCoordinates( indices, false );
//vertices.set(barycentric, konOff);
//var konOff = nv*12;
vertices.set(v, konOff);
konOff += nv*12;
if(m.vertex.texCoord) {
var uv = view.subarray(off, off + nv*8);
vertices.set(uv, konOff);
konOff += nv*8;
off += nv*8;
}
if(m.vertex.normal && m.vertex.color) {
var no = view.subarray(off, off + nv*6);
var co = view.subarray(off + nv*6, off + nv*6 + nv*4);
vertices.set(co, konOff );
vertices.set(no, konOff + nv*4);
}
else {
if(m.vertex.normal) {
var no = view.subarray(off, off + nv*6);
vertices.set(no, off);
}
if(m.vertex.color) {
var co = view.subarray(off, off + nv*4);
vertices.set(co, off);
}
}
var gl = node.context.gl;
var vbo = m.vbo[n] = gl.createBuffer();
gl.bindBuffer(gl.ARRAY_BUFFER, vbo);
gl.bufferData(gl.ARRAY_BUFFER, vertices, gl.STATIC_DRAW);
var ibo = m.ibo[n] = gl.createBuffer();
gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, ibo);
gl.bufferData(gl.ELEMENT_ARRAY_BUFFER, indices, gl.STATIC_DRAW);
}
Original code does not have barycentric part and without it, it all works. What i don't understand is how to correctly add barycentric data to the "vertices" array to pass it to the shader. The code above doesn't crash, but it does cause UVs to be out of whack. Barycentric coordinates are just a vec3, similar to position. They are just 1s and 0s. As i understand, 1 per vertex. I think I should be able to pack them in the "vertices" array with correct offsets. I even modified the above code to pass in positions instead of barycentric data, and it still doesn't work (it casues UVs to be out whack). Not sure if this enough context to reason about it.
Am i doing something wrong with offsets?
Also, do I need to de-index my data for this to work? Wireframe library does do that.
Let me know if there is more info I can provide.
P.S. Nexus is a chunking / LODing system. It loads patches over time. As far as i understand it's only one "mesh" object, it just adds more data to the buffers as it downloads it.