Prof. Hart's
JavaScript
Tryer Outer

<!DOCTYPE HTML> 
<html>

var vertexShaderSource = 
    "attribute vec3 aVertexPosition;                 \n" +
    "void main() {                                   \n" +
    "  gl_Position = vec4(aVertexPosition, 1.0);     \n" +
    "}                                               \n";

var vertexShader = gl.createShader(gl.VERTEX_SHADER);
  gl.shaderSource(vertexShader, vertexShaderSource);
  gl.compileShader(vertexShader);
  if (!gl.getShaderParameter(vertexShader, gl.COMPILE_STATUS)) alert(gl.getShaderInfoLog(vertexShader));
   
  var fragmentShaderSource = 
     "precision mediump float;                    \n"+
     "void main() {                               \n"+
     "  gl_FragColor = vec4(1.0, 1.0, 1.0, 1.0);  \n"+
     "}                                           \n";

var fragmentShader = gl.createShader(gl.FRAGMENT_SHADER);
  gl.shaderSource(fragmentShader, fragmentShaderSource);
  gl.compileShader(fragmentShader);
  if (!gl.getShaderParameter(fragmentShader, gl.COMPILE_STATUS))
    alert(gl.getShaderInfoLog(fragmentShader));
     
  var shaderProgram = gl.createProgram();
  gl.attachShader(shaderProgram, vertexShader);
  gl.attachShader(shaderProgram, fragmentShader);
  gl.linkProgram(shaderProgram);
  if (!gl.getProgramParameter(shaderProgram, gl.LINK_STATUS))
    alert("Failed to setup shaders");
  gl.useProgram(shaderProgram);
  shaderProgram.vertexPositionAttribute = gl.getAttribLocation(shaderProgram, "aVertexPosition");

var vertexBuffer = gl.createBuffer();
  gl.bindBuffer(gl.ARRAY_BUFFER, vertexBuffer);
  var triangleVertices = [
         0.0,  0.5,  0.0,
        -0.5, -0.5,  0.0,
         0.5, -0.5,  0.0
  ];
  gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(triangleVertices), gl.STATIC_DRAW);
  vertexBuffer.itemSize = 3;
  vertexBuffer.numberOfItems = 3;

gl.clearColor(0.0, 0.0, 0.0, 1.0);
  gl.clear(gl.COLOR_BUFFER_BIT);
  
  gl.vertexAttribPointer(shaderProgram.vertexPositionAttribute, 
                         vertexBuffer.itemSize, gl.FLOAT, false, 0, 0);
  gl.enableVertexAttribArray(shaderProgram.vertexPositionAttribute);
  gl.drawArrays(gl.TRIANGLES, 0, vertexBuffer.numberOfItems);
}
</script>

</html>