extract error reporting/displaying to a function

glsl/raymarching.js

// - [WebGL Fundamentals](http://webglfundamentals.org/webgl/lessons/webgl-fundamentals.html)
try {
  document.body.style = "margin: 0; overflow: hidden;";
  document.body.innerHTML = "";
  
  var errorEl = document.createElement("pre");
  errorEl.style = "color: red; position: absolute; right: 0; bottom: 0;";
  document.body.appendChild(errorEl);
  
  function displayError(e) {
    window.error = e;
    errorEl.textContent = e;
  }
  
  function compileShader(gl, type, shaderSrc) {
    var shader = gl.createShader(type);
    gl.shaderSource(shader, shaderSrc);
  gl_FragColor = vec4( col, 1.0 );
}
`
  
  document.body.style = "margin: 0; overflow: hidden;";
  document.body.innerHTML = "";
  
   
  var styleEl = document.createElement("style");
  styleEl.textContent = `
  
  tt.render();
} catch (e) {
  window.error = e;
  var msg = document.createElement("pre");
  msg.style = "color: red; position: absolute; right: 0; bottom: 0";
  msg.textContent = e;
  document.body.appendChild(msg);
  displayError(e);
}