basic_error_handler.js

// @license magnet:?xt=urn:btih:8e4f440f4c65981c5bf93c76d35135ba5064d8b7&dn=apache-2.0.txt Apache-2.0

/* Copyright 2021 Richard Hansen <rhansen@rhansen.org> */

'use strict';

// Set up an error handler to display errors that happen during page load. This handler will be
// overridden with a nicer handler by setupGlobalExceptionHandler() in pad_utils.js.

(() => {
  const originalHandler = window.onerror;
  window.onerror = (...args) => {
    const [msg, url, line, col, err] = args;

    // Purge the existing HTML and styles for a consistent view.
    document.body.textContent = '';
    for (const el of document.querySelectorAll('head style, head link[rel="stylesheet"]')) {
      el.remove();
    }

    const box = document.body;
    box.textContent = '';
    const summary = document.createElement('p');
    box.appendChild(summary);
    summary.appendChild(document.createTextNode('An error occurred while loading the page:'));
    const msgBlock = document.createElement('blockquote');
    box.appendChild(msgBlock);
    msgBlock.style.fontWeight = 'bold';
    msgBlock.appendChild(document.createTextNode(msg));
    const loc = document.createElement('p');
    box.appendChild(loc);
    loc.appendChild(document.createTextNode(`in ${url}`));
    loc.appendChild(document.createElement('br'));
    loc.appendChild(document.createTextNode(`at line ${line}:${col}`));
    const stackSummary = document.createElement('p');
    box.appendChild(stackSummary);
    stackSummary.appendChild(document.createTextNode('Stack trace:'));
    const stackBlock = document.createElement('blockquote');
    box.appendChild(stackBlock);
    const stack = document.createElement('pre');
    stackBlock.appendChild(stack);
    stack.appendChild(document.createTextNode(err.stack || err.toString()));

    if (typeof originalHandler === 'function') originalHandler(...args);
  };
})();

// @license-end