code: function initShaders() {
    var fragmentShader = getShader(gl, fragmentShaderSource, false);
    var vertexShader = getShader(gl, vertexShaderSource, true);
  
    // Create the shader program
  
    shaderProgram = gl.createProgram();
    gl.attachShader(shaderProgram, vertexShader);
    gl.attachShader(shaderProgram, fragmentShader);
    gl.linkProgram(shaderProgram);
  
    // If creating the shader program failed, alert
  
    if (!gl.getProgramParameter(shaderProgram, gl.LINK_STATUS)) {
      alert("Unable to initialize the shader program: " + gl.getProgramInfoLog(shader));
    }
  
    gl.useProgram(shaderProgram);
  
    vertexPositionAttribute = gl.getAttribLocation(shaderProgram, "aVertexPosition");
    gl.enableVertexAttribArray(vertexPositionAttribute);
  }
docs: initShaders  Initialize the shaders, so WebGL knows how to light our scene.