i am trying to run this code in a json script, its just the webgl code. I am trying to make this work but it doesnt. I am trying to make an octagon using mulptiple triangles but when im trying to create them with the indexes it does not work.

I think the problem is at the indexes numItems value. It is also supposed to show a black backround but this doesnt show either. Any help? (this is not the whole code but i figure here is where the problem is)

  octagonIndexBuffer = gl.createBuffer(); // **
gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, octagonIndexBuffer); // We bind the IBO as an ELEMENT_ARRAY_BUFFER.
let indexes = [ // The indexes that will be loaded in the buffer
    0, 2, 4,//A
    4, 0, 6,//B
    6, 0, 7,//C
    7, 0, 5,//D
    5, 0, 3,//E
    5, 0, 8,//F
    8, 0, 9,//G
    9, 0, 2//H
];

gl.bufferData(gl.ELEMENT_ARRAY_BUFFER, new Uint16Array(indexes), gl.STATIC_DRAW);
octagonIndexBuffer.itemSize = 1; // item size = 1 because one index = one vertex.
octagonIndexBuffer.numItems = 24;

  octagonVertexColorBuffer = gl.createBuffer();
gl.bindBuffer(gl.ARRAY_BUFFER, octagonVertexColorBuffer);

// We define our vertex colors.
let colors = [
    0.0, 1.0, 0.0, 1.0,
    1.0, 0.0, 0.0, 1.0,
    0.0, 0.0, 1.0, 1.0,
    0.0, 1.0, 0.0, 1.0,
    1.0, 0.0, 0.0, 1.0,
    0.0, 0.0, 1.0, 1.0,
    0.0, 1.0, 0.0, 1.0,
    1.0, 0.0, 0.0, 1.0,
    0.0, 0.0, 0.0, 1.0
];
gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(colors), gl.STATIC_DRAW);
octagonVertexColorBuffer.itemSize = 4; // item size = 4 because (R, G, B, A).
octagonVertexColorBuffer.numItems = 9;

    octagonVertexPositionBuffer = gl.createBuffer(); // We tell our GPU to create a buffer and give us a pointer to it.
gl.bindBuffer(gl.ARRAY_BUFFER, octagonVertexPositionBuffer); // We need to bind the buffer (make it active) in order to use it.

// We define our vertex positions.
let vertices = [
     0.0, 0.0, 0.0,   //1
     1.0,  1.0,  0.0,//2
    -1.0, 1.0,  0.0, //3
     1.0, -1.0,  0.0,//4
    -1.0, -1.0, 0.0,  //5
     0.5, -1.5,  0.0, //6
    -0.5, -1.5, 0.0 , //7
    -0.5, 1.5, 0.0 ,  //8
     0.5, 1.5, 0.0  , //9

];
gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(vertices), gl.STATIC_DRAW); // We send the vertex positions to the buffer in our GPU.
octagonVertexColorBufferVertexPositionBuffer.itemSize = 3; // item size = 3 because (x, y, z).
octagonVertexPositionBuffer.numItems = 9; // numItems = 3 because we have three vertices.