mojibake-fixer

osamurai-mojibake-fix.user.js

// ==UserScript==
// @name         Osamurai Mojibake Fix
// @namespace    https://osamurai.azimech.net/
// @version      1.0.0
// @description  Fix UTF-8 mojibake on osamurai.azimech.net pages.
// @match        https://osamurai.azimech.net/*
// @run-at       document-end
// @grant        none
// ==/UserScript==

(() => {
  'use strict';

  const fixableAttributes = new Set([
    'alt',
    'aria-label',
    'content',
    'placeholder',
    'title',
  ]);

  const fixMojibake = value => {
    if (typeof value !== 'string' || value === '') {
      return value;
    }

    try {
      const bytes = Uint8Array.from(value, character => {
        const code = character.charCodeAt(0);
        if (code > 255) {
          throw new RangeError('not single-byte mojibake');
        }
        return code;
      });
      return new TextDecoder('utf-8', { fatal: true }).decode(bytes);
    } catch {
      return value;
    }
  };

  const fixTextNodes = root => {
    const walker = document.createTreeWalker(root, NodeFilter.SHOW_TEXT);
    let node;

    while ((node = walker.nextNode())) {
      node.nodeValue = fixMojibake(node.nodeValue);
    }
  };

  const fixAttributes = root => {
    for (const element of root.querySelectorAll('*')) {
      for (const attribute of element.attributes) {
        if (fixableAttributes.has(attribute.name)) {
          element.setAttribute(attribute.name, fixMojibake(attribute.value));
        }
      }
    }
  };

  const fixRoot = root => {
    fixTextNodes(root);
    fixAttributes(root);
  };

  fixRoot(document.body);

  new MutationObserver(mutations => {
    for (const mutation of mutations) {
      for (const node of mutation.addedNodes) {
        if (node.nodeType === Node.TEXT_NODE) {
          node.nodeValue = fixMojibake(node.nodeValue);
        } else if (node.nodeType === Node.ELEMENT_NODE) {
          fixRoot(node);
        }
      }

      if (mutation.type === 'attributes' && fixableAttributes.has(mutation.attributeName)) {
        const value = mutation.target.getAttribute(mutation.attributeName);
        mutation.target.setAttribute(mutation.attributeName, fixMojibake(value));
      }
    }
  }).observe(document.body, {
    attributeFilter: [...fixableAttributes],
    attributes: true,
    childList: true,
    subtree: true,
  });
})();