code: function createShaderFromScript(
        gl, scriptId, opt_shaderType, opt_errorCallback) {
      var shaderSource = "";
      var shaderType;
      var shaderScript = document.getElementById(scriptId);
      if (!shaderScript) {
        throw ("*** Error: unknown script element" + scriptId);
      }
      shaderSource = shaderScript.text;
  
      if (!opt_shaderType) {
        if (shaderScript.type === "x-shader/x-vertex") {
          shaderType = gl.VERTEX_SHADER;
        } else if (shaderScript.type === "x-shader/x-fragment") {
          shaderType = gl.FRAGMENT_SHADER;
        } else if (shaderType !== gl.VERTEX_SHADER && shaderType !== gl.FRAGMENT_SHADER) {
          throw ("*** Error: unknown shader type");
        }
      }
  
      return loadShader(
          gl, shaderSource, opt_shaderType ? opt_shaderType : shaderType,
          opt_errorCallback);
    }
docs: Loads a shader from a script tag.
  @param {WebGLRenderingContext} gl The WebGLRenderingContext to use.
  @param {string} scriptId The id of the script tag.
  @param {number} opt_shaderType The type of shader. If not passed in it will
  be derived from the type of the script tag.
  @param {module:webgl-utils.ErrorCallback} opt_errorCallback callback for errors.
  @return {WebGLShader} The created shader.