I know it's more of a javascript-problem, but I have troubles moving the global "vertexBlaBuffer" variables over to the scope of the Geometry prototype:
Code :
function Geometry(position, rotation, path) {
	this.position = position;
	this.rotation = rotation;
	this.path = path;
 
	var request = new XMLHttpRequest();
	request.open("GET", path);
	request.onreadystatechange = function() {
		if (request.readyState == 4) {
			handleLoadedModel(JSON.parse(request.responseText));
		}
	}
	request.send();
 
	initTextures();
}
 
/******************************************************************************
 * FUNCTION: handleLoadedModel
 *	Load extracted model data into GL buffers
 ******************************************************************************/
var vertexPositionBuffer;
var vertexNormalBuffer;
var vertexTextureCoordBuffer;
var vertexIndexBuffer;
function handleLoadedModel(modelData) {
	vertexNormalBuffer = gl.createBuffer();
	gl.bindBuffer(gl.ARRAY_BUFFER, vertexNormalBuffer);
	gl.bufferData(gl.ARRAY_BUFFER, new WebGLFloatArray(modelData.vertexNormals), gl.STATIC_DRAW);
	vertexNormalBuffer.itemSize = 3;
	vertexNormalBuffer.numItems = modelData.vertexNormals.length / 3;
 
	vertexTextureCoordBuffer = gl.createBuffer();
	gl.bindBuffer(gl.ARRAY_BUFFER, vertexTextureCoordBuffer);
	gl.bufferData(gl.ARRAY_BUFFER, new WebGLFloatArray(modelData.vertexTextureCoords), gl.STATIC_DRAW);
	vertexTextureCoordBuffer.itemSize = 2;
	vertexTextureCoordBuffer.numItems = modelData.vertexTextureCoords.length / 2;
 
	vertexPositionBuffer = gl.createBuffer();
	gl.bindBuffer(gl.ARRAY_BUFFER, vertexPositionBuffer);
	gl.bufferData(gl.ARRAY_BUFFER, new WebGLFloatArray(modelData.vertexPositions), gl.STATIC_DRAW);
	vertexPositionBuffer.itemSize = 3;
	vertexPositionBuffer.numItems = modelData.vertexPositions.length / 3;
 
	vertexIndexBuffer = gl.createBuffer();
	gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, vertexIndexBuffer);
	gl.bufferData(gl.ELEMENT_ARRAY_BUFFER, new WebGLUnsignedShortArray(modelData.indices), gl.STREAM_DRAW);
	vertexIndexBuffer.itemSize = 1;
	vertexIndexBuffer.numItems = modelData.indices.length;
}

I already tried binding the buffers in the anonymous onreadystatechange function of the request, but in that scope, "this" doesn't seem to refer to Geometry.
Any tips?