original https://github.com/fukayatsu/esarea

esarea.js

// ==UserScript==
// @name         esarea
// @namespace    esarea
// @version      0.1
// @description  try to take over the world!
// @author       esa
// @match        https://ghe.ckpd.co/*
// @icon         https://www.google.com/s2/favicons?sz=64&domain=github.com
// @grant        none
// @require      https://ajax.googleapis.com/ajax/libs/jquery/3.6.0/jquery.min.js
// @require      https://raw.githubusercontent.com/madapaja/jquery.selection/master/src/jquery.selection.js
// ==/UserScript==

(function() {
  'use strict';
  /*
 * decaffeinate suggestions:
 * DS101: Remove unnecessary use of Array.from
 * DS102: Remove unnecessary code created because of implicit returns
 * DS209: Avoid top-level return
 * Full docs: https://github.com/decaffeinate/decaffeinate/blob/main/docs/suggestions.md
 */

  if (location.host.match(/scrapbox\.io|qiita\.com|esa\.io|docbase\.io|pplog\.net|lvh\.me|slack\.com|mimemo\.io|kibe\.la|hackmd\.io/)) { return; }

  let suggesting = null;
  $(document).on('keyup', 'textarea', function(e) {
    if (location.host.match(/github\.com/)) {
      suggesting = !!$('ul.suggestions:visible').length;
    } else if (location.host.match(/idobata\.io/)) {
      suggesting = !!$('.atwho-view:visible').length;
    }
  });

  $(document).on('keydown', 'textarea', function(e) {
    if (suggesting) { return; }

    switch (e.which || e.keyCode) {
      case 9:
        handleTabKey(e);
        break;
      case 13:
        handleEnterKey(e);
        break;
      case 32:
        handleSpaceKey(e);
        break;
    }
  });

  var handleTabKey = function(e) {
    let newPos;
    e.preventDefault();
    const currentLine = getCurrentLine(e);
    const text = $(e.target).val();
    const pos  = $(e.target).selection('getPos');
    if (currentLine) { $(e.target).selection('setPos', {start: currentLine.start, end: currentLine.end}); }
    if (e.shiftKey) {
      if (currentLine && (currentLine.text.charAt(0) === '|')) {
        // prev cell in table
        newPos = text.lastIndexOf('|', pos.start - 1);
        if (newPos > 1) { newPos -= 1; }
        $(e.target).selection('setPos', {start: newPos, end: newPos});
      } else {
        // re indent
        const reindentedText  = $(e.target).selection().replace(/^ {1,4}/gm, '');
        const reindentedCount = $(e.target).selection().length - reindentedText.length;
        replaceText(e.target, reindentedText);
        if (currentLine) {
          $(e.target).selection('setPos', {start: pos.start - reindentedCount, end: pos.start - reindentedCount});
        } else {
          $(e.target).selection('setPos', {start: pos.start, end: pos.start + reindentedText.length});
        }
      }

    } else {
      if (currentLine && (currentLine.text.charAt(0) === '|')) {
        // next cell in table
        newPos = text.indexOf('|', pos.start + 1);
        if ((newPos < 0) || (newPos === text.lastIndexOf('|', currentLine.end - 1))) {
          $(e.target).selection('setPos', {start: currentLine.end, end: currentLine.end});
        } else {
          $(e.target).selection('setPos', {start: newPos + 2, end: newPos + 2 });
        }
      } else {
        // indent
        const indentedText = '    ' + $(e.target).selection().split("\n").join("\n    ");
        replaceText(e.target, indentedText);
        if (currentLine) {
          $(e.target).selection('setPos', {start: pos.start + 4, end: pos.start + 4});
        } else {
          $(e.target).selection('setPos', {start: pos.start, end: pos.start + indentedText.length});
        }
      }
    }
    return $(e.target).trigger('input');
  };

  var handleEnterKey = function(e) {
    let currentLine, match;
    if (e.metaKey || e.ctrlKey || e.shiftKey) { return; } // for cmd + enter
    if (!(currentLine = getCurrentLine(e))) { return; }
    if (currentLine.start === currentLine.caret) { return; }
    if (match = currentLine.text.match(/^(\s*(?:-|\+|\*|\d+\.) (?:\[(?:x| )\] )?)\s*\S/)) {
      // smart indent with list
      let listMarkMatch;
      if (currentLine.text.match(/^(\s*(?:-|\+|\*|\d+\.) (?:\[(?:x| )\] ))\s*$/)) {
        // empty task list
        $(e.target).selection('setPos', {start: currentLine.start, end: (currentLine.end - 1)});
        return;
      }
      e.preventDefault();
      let listMark = match[1].replace(/\[x\]/, '[ ]');
      if (listMarkMatch = listMark.match(/^(\s*)(\d+)\./)) {
        const indent = listMarkMatch[1];
        const num    = parseInt(listMarkMatch[2]);
        if (num !== 1) { listMark = listMark.replace(/\s*\d+/, `${indent}${num + 1}`); }
      }
      replaceText(e.target, "\n" + listMark);
      const caretTo = currentLine.caret + listMark.length + 1;
      $(e.target).selection('setPos', {start: caretTo, end: caretTo});
    } else if (currentLine.text.match(/^(\s*(?:-|\+|\*|\d+\.) )/)) {
      // remove list
      $(e.target).selection('setPos', {start: currentLine.start, end: (currentLine.end)});
    } else if (currentLine.text.match(/^.*\|\s*$/)) {
      // new row for table
      if (currentLine.text.match(/^[\|\s]+$/)) {
        $(e.target).selection('setPos', {start: currentLine.start, end: (currentLine.end)});
        return;
      }
      if (!currentLine.endOfLine) { return; }
      e.preventDefault();
      const row = [];
      for (match of Array.from(currentLine.text.match(/\|/g))) { row.push("|"); }
      const prevLine = getPrevLine(e);
      if (!prevLine || (!currentLine.text.match(/---/) && !prevLine.text.match(/\|/g))) {
        replaceText(e.target, "\n" + row.join(' --- ') + "\n" + row.join('  '));
        $(e.target).selection('setPos', {start: (currentLine.caret + (6 * row.length)) - 1, end: (currentLine.caret + (6 * row.length)) - 1});
      } else {
        replaceText(e.target, "\n" + row.join('  '));
        $(e.target).selection('setPos', {start: currentLine.caret + 3, end: currentLine.caret + 3 });
      }
    }
    return $(e.target).trigger('input');
  };

  var handleSpaceKey = function(e) {
    let currentLine, match;
    if (!e.shiftKey || !e.altKey) { return; }
    if (!(currentLine = getCurrentLine(e))) { return; }
    if (match = currentLine.text.match(/^(\s*)(-|\+|\*|\d+\.) (?:\[(x| )\] )(.*)/)) {
      e.preventDefault();
      const checkMark = match[3] === ' ' ? 'x' : ' ';
      const replaceTo = `${match[1]}${match[2]} [${checkMark}] ${match[4]}`;
      $(e.target).selection('setPos', {start: currentLine.start, end: currentLine.end});
      replaceText(e.target, replaceTo);
      $(e.target).selection('setPos', {start: currentLine.caret, end: currentLine.caret});
      return $(e.target).trigger('input');
    }
  };

  var getCurrentLine = function(e) {
    const text = $(e.target).val();
    const pos  = $(e.target).selection('getPos');

    if (!text) { return null; }
    if (pos.start !== pos.end) { return null; }

    const startPos = text.lastIndexOf("\n", pos.start - 1) + 1;
    let endPos   = text.indexOf("\n", pos.start);
    if (endPos === -1) { endPos   = text.length; }
    return {
      text:  text.slice(startPos, endPos),
      start: startPos,
      end:   endPos,
      caret: pos.start,
      endOfLine: !$.trim(text.slice(pos.start, endPos))
    };
  };

  var getPrevLine = function(e) {
    const currentLine = getCurrentLine(e);
    const text = $(e.target).val().slice(0, currentLine.start);

    const startPos = text.lastIndexOf("\n", currentLine.start - 2) + 1;
    const endPos   = currentLine.start;
    return {
      text:  text.slice(startPos, endPos),
      start: startPos,
      end:   endPos
    };
  };

  // @see https://mimemo.io/m/mqLXOlJe7ozQ19r
  var replaceText = function(target, str) {
    let e;
    const pos = $(target).selection('getPos');
    const fromIdx = pos.start;
    const toIdx   = pos.end;
    let inserted = false;

    if (str) {
      const expectedLen = (target.value.length - Math.abs(toIdx - fromIdx)) + str.length;
      target.focus();
      target.selectionStart = fromIdx;
      target.selectionEnd = toIdx;
      try {
        inserted = document.execCommand('insertText', false, str);
      } catch (error) {
        e = error;
        inserted = false;
      }
      if (inserted && ((target.value.length !== expectedLen) || (target.value.substr(fromIdx, str.length) !== str))) {
        //firefoxでなぜかうまくいってないくせにinsertedがtrueになるので失敗を検知してfalseに…
        inserted = false;
      }
    }
    if (!inserted) {
      try {
        document.execCommand('ms-beginUndoUnit');
      } catch (error1) { e = error1; }
      const {
        value
      } = target;
      target.value = '' + value.substring(0, fromIdx) + str + value.substring(toIdx);
      try {
        document.execCommand('ms-endUndoUnit');
      } catch (error2) { e = error2; }
    }
    $(target).trigger('blur').trigger('focus');
  };

})();