code: function loadShader(gl, shaderSource, shaderType, opt_errorCallback) {
      var errFn = opt_errorCallback || error;
      // Create the shader object
      var shader = gl.createShader(shaderType);
  
      // Load the shader source
      gl.shaderSource(shader, shaderSource);
  
      // Compile the shader
      gl.compileShader(shader);
  
      // Check the compile status
      var compiled = gl.getShaderParameter(shader, gl.COMPILE_STATUS);
      if (!compiled) {
        // Something went wrong during compilation; get the error
        var lastError = gl.getShaderInfoLog(shader);
        errFn("*** Error compiling shader '" + shader + "':" + lastError);
        gl.deleteShader(shader);
        return null;
      }
  
      return shader;
    }
docs: Error Callback
  @callback ErrorCallback
  @param {string} msg error message.
  @memberOf module:webgl-utils
   
  Loads a shader.
  @param {WebGLRenderingContext} gl The WebGLRenderingContext to use.
  @param {string} shaderSource The shader source.
  @param {number} shaderType The type of shader.
  @param {module:webgl-utils.ErrorCallback} opt_errorCallback callback for errors.
  @return {WebGLShader} The created shader.