Add editor experience features: auto-run, layouts, resizable panels, Emmet, vim/emacs

- Auto-run toggle with localStorage persistence (toolbar checkbox)
- Layout selector: default, top/bottom, editor-only, preview-only
- Resizable panels via drag dividers with double-click reset
- Emmet abbreviation expansion for HTML, CSS, and JSX
- Vim and Emacs keybinding modes with lazy-loaded CDN libraries
- Shared preferences module for localStorage management
- Editor hooks for tab switch and mode change callbacks

public/css/style.css

@@ -47,11 +47,11 @@ button:hover { background: var(--accent-hover); }
 }
 .btn-small:hover { color: var(--text); background: var(--border); }
 
-/* Grid layout — 2 columns: editor | preview+console */
+/* Grid layout — 2 columns with dividers: editor | divider | preview+console */
 .grid {
   display: grid;
-  grid-template-columns: 1fr 1fr;
+  grid-template-columns: 1fr 4px 1fr;
-  grid-template-rows: 1fr 1fr;
+  grid-template-rows: 1fr 4px 1fr;
   height: calc(100vh - var(--toolbar-h));
 }
 .panel { position: relative; border: 1px solid var(--border); overflow: hidden; display: flex; flex-direction: column; }
@@ -65,9 +65,39 @@ button:hover { background: var(--accent-hover); }
 }
 
 /* Editor panel — full left column */
-.panel-editor  { grid-column: 1; grid-row: 1 / 3; display: flex; flex-direction: column; }
+.panel-editor  { grid-column: 1; grid-row: 1 / 4; display: flex; flex-direction: column; }
-.panel-preview { grid-column: 2; grid-row: 1; }
+.divider-col   { grid-column: 2; grid-row: 1 / 4; cursor: col-resize; background: var(--border); }
-.panel-console { grid-column: 2; grid-row: 2; }
+.divider-col:hover { background: var(--accent); }
+.panel-preview { grid-column: 3; grid-row: 1; }
+.divider-row   { grid-column: 3; grid-row: 2; cursor: row-resize; background: var(--border); }
+.divider-row:hover { background: var(--accent); }
+.panel-console { grid-column: 3; grid-row: 3; }
+
+/* Disable iframe pointer-events while dragging */
+body.resizing iframe { pointer-events: none; }
+
+/* Layout variants */
+.layout-top-bottom .panel-editor  { grid-column: 1 / 4; grid-row: 1; }
+.layout-top-bottom .divider-col   { display: none; }
+.layout-top-bottom .panel-preview { grid-column: 1; grid-row: 3; }
+.layout-top-bottom .divider-row   { grid-column: 1 / 4; grid-row: 2; cursor: row-resize; }
+.layout-top-bottom .panel-console { grid-column: 2 / 4; grid-row: 3; }
+.layout-top-bottom {
+  grid-template-columns: 1fr 4px 1fr;
+  grid-template-rows: 1fr 4px 1fr;
+}
+
+.layout-editor-only .panel-editor  { grid-column: 1 / 4; grid-row: 1 / 4; }
+.layout-editor-only .divider-col,
+.layout-editor-only .divider-row,
+.layout-editor-only .panel-preview,
+.layout-editor-only .panel-console { display: none; }
+
+.layout-preview-only .panel-preview { grid-column: 1 / 4; grid-row: 1 / 4; }
+.layout-preview-only .divider-col,
+.layout-preview-only .divider-row,
+.layout-preview-only .panel-editor,
+.layout-preview-only .panel-console { display: none; }
 
 /* Tab bar */
 .tab-bar {
@@ -139,6 +169,41 @@ button:hover { background: var(--accent-hover); }
 .console-info { color: #3dc9b0; }
 .console-debug { color: #888; }
 
+/* Vim status bar */
+.vim-status-bar {
+  display: none;
+  height: 24px;
+  line-height: 24px;
+  padding: 0 10px;
+  font-family: 'Cascadia Code', 'Fira Code', monospace;
+  font-size: 12px;
+  background: var(--surface);
+  color: var(--text-dim);
+  border-top: 1px solid var(--border);
+  flex-shrink: 0;
+}
+
+/* Auto-run toggle */
+.auto-run-toggle {
+  display: flex;
+  align-items: center;
+  gap: 4px;
+  font-size: 12px;
+  color: var(--text-dim);
+  cursor: pointer;
+  user-select: none;
+}
+.auto-run-toggle input { cursor: pointer; }
+
+/* Dividers */
+.divider { background: var(--border); transition: background 0.15s; z-index: 2; }
+
+/* Layout/keybinding selects — match framework select */
+#layout-mode, #keybinding-mode {
+  background: var(--bg); color: var(--text); border: 1px solid var(--border);
+  padding: 4px 6px; border-radius: 4px; font-size: 12px; cursor: pointer;
+}
+
 /* Toast */
 .toast {
   position: fixed; bottom: 20px; left: 50%; transform: translateX(-50%);

public/index.html

@@ -19,8 +19,23 @@
         <option value="svelte">Svelte</option>
       </select>
       <input type="text" id="title-input" placeholder="Untitled" spellcheck="false">
+      <select id="layout-mode">
+        <option value="default">Default</option>
+        <option value="top-bottom">Top / Bottom</option>
+        <option value="editor-only">Editor Only</option>
+        <option value="preview-only">Preview Only</option>
+      </select>
+      <select id="keybinding-mode">
+        <option value="default">Default</option>
+        <option value="vim">Vim</option>
+        <option value="emacs">Emacs</option>
+      </select>
     </div>
     <div class="toolbar-right">
+      <label class="auto-run-toggle" title="Auto-run on change">
+        <input type="checkbox" id="auto-run-checkbox" checked>
+        Auto
+      </label>
       <button id="btn-run" title="Run (Ctrl+Enter)">Run</button>
       <button id="btn-save" title="Save (Ctrl+S)">Save</button>
       <button id="btn-fork" title="Fork">Fork</button>
@@ -31,11 +46,14 @@
     <div class="panel panel-editor">
       <div class="tab-bar" id="tab-bar"></div>
       <div id="editor-area" class="editor-area"></div>
+      <div id="vim-status-bar" class="vim-status-bar"></div>
     </div>
+    <div class="divider divider-col" id="divider-col"></div>
     <div class="panel panel-preview">
       <div class="panel-label">Preview</div>
       <iframe id="preview-frame" sandbox="allow-scripts allow-same-origin"></iframe>
     </div>
+    <div class="divider divider-row" id="divider-row"></div>
     <div class="panel panel-console">
       <div class="panel-label">Console <button id="btn-clear-console" class="btn-small">Clear</button></div>
       <div id="console-output"></div>

public/js/app.js

@@ -1,6 +1,7 @@
 import {
   initEditors, switchMode, getEditorValues, setEditorValues,
   setOnChange, getCurrentMode, getCssType, setCssType,
+  relayoutEditors,
   MODE_TABS, MODE_TO_JS_TYPE, JS_TYPE_TO_MODE,
 } from './editors.js';
 import { renderPreview } from './preview.js';
@@ -8,6 +9,10 @@ import { initConsole, clearConsole } from './console-panel.js';
 import { compileCss } from './preprocessors.js';
 import { compileJs } from './js-preprocessors.js';
 import { createFiddle, loadFiddle, updateFiddle } from './api.js';
+import { getPref, setPref } from './preferences.js';
+import { initEmmet } from './emmet.js';
+import { initKeybindings } from './keybindings.js';
+import { initResizer, clearInlineSizes } from './resizer.js';
 
 let currentId = null;
 let debounceTimer = null;
@@ -67,6 +72,7 @@ async function run() {
 }
 
 function scheduleRun() {
+  if (!getPref('autoRun')) return;
   clearTimeout(debounceTimer);
   debounceTimer = setTimeout(run, 500);
 }
@@ -155,10 +161,43 @@ function handleModeChange(newMode) {
   scheduleRun();
 }
 
-function init() {
+function applyLayout(layout) {
+  const grid = $('.grid');
+  // Remove all layout classes
+  grid.classList.remove('layout-top-bottom', 'layout-editor-only', 'layout-preview-only');
+  // Clear resizer inline styles when switching layouts
+  clearInlineSizes();
+
+  if (layout === 'top-bottom') grid.classList.add('layout-top-bottom');
+  else if (layout === 'editor-only') grid.classList.add('layout-editor-only');
+  else if (layout === 'preview-only') grid.classList.add('layout-preview-only');
+
+  setPref('layout', layout);
+  // Give DOM time to reflow then relayout editors
+  requestAnimationFrame(() => relayoutEditors());
+}
+
+async function init() {
+  // Load Emmet before editors so completion providers are registered
+  await initEmmet();
+
   initEditors('html-css-js');
   setOnChange(scheduleRun);
   initConsole();
+  initResizer();
+  initKeybindings();
+
+  // Auto-run checkbox
+  const autoRunCb = $('#auto-run-checkbox');
+  autoRunCb.checked = getPref('autoRun');
+  autoRunCb.addEventListener('change', (e) => setPref('autoRun', e.target.checked));
+
+  // Layout selector
+  const layoutSel = $('#layout-mode');
+  const savedLayout = getPref('layout') || 'default';
+  layoutSel.value = savedLayout;
+  if (savedLayout !== 'default') applyLayout(savedLayout);
+  layoutSel.addEventListener('change', (e) => applyLayout(e.target.value));
 
   // Mode selector
   $('#framework-mode').addEventListener('change', (e) => {

public/js/editors.js

@@ -61,6 +61,8 @@ let currentMode = 'html-css-js';
 let activeTab = null;
 let cssType = 'css';
 let onChangeCallback = null;
+let onTabSwitchCallback = null;
+let onModeChangeCallback = null;
 
 const tabBar = () => document.getElementById('tab-bar');
 const editorArea = () => document.getElementById('editor-area');
@@ -69,6 +71,27 @@ export function setOnChange(cb) {
   onChangeCallback = cb;
 }
 
+export function setOnTabSwitch(cb) {
+  onTabSwitchCallback = cb;
+}
+
+export function setOnModeChange(cb) {
+  onModeChangeCallback = cb;
+}
+
+export function getActiveEditor() {
+  if (activeTab && editors[activeTab]) return editors[activeTab];
+  return null;
+}
+
+export function relayoutEditors() {
+  const tabs = MODE_TABS[currentMode];
+  if (!tabs) return;
+  tabs.forEach((tab) => {
+    if (editors[tab.id]) editors[tab.id].layout();
+  });
+}
+
 export function getCurrentMode() {
   return currentMode;
 }
@@ -213,6 +236,8 @@ export function switchMode(mode) {
   });
 
   switchTab(tabs[0].id);
+
+  if (onModeChangeCallback) onModeChangeCallback(mode);
 }
 
 export function switchTab(tabId) {
@@ -237,6 +262,8 @@ export function switchTab(tabId) {
     editors[tabId].layout();
     editors[tabId].focus();
   }
+
+  if (onTabSwitchCallback) onTabSwitchCallback(tabId, editors[tabId]);
 }
 
 export function getEditorValues() {

public/js/emmet.js

@@ -0,0 +1,29 @@
+let loaded = false;
+
+function loadScript(src) {
+  return new Promise((resolve, reject) => {
+    if (document.querySelector(`script[src="${src}"]`)) { resolve(); return; }
+    const savedDefine = window.define;
+    window.define = undefined;
+    const s = document.createElement('script');
+    s.src = src;
+    s.onload = () => { window.define = savedDefine; resolve(); };
+    s.onerror = () => { window.define = savedDefine; reject(new Error(`Failed to load ${src}`)); };
+    document.head.appendChild(s);
+  });
+}
+
+export async function initEmmet() {
+  if (loaded) return;
+  try {
+    await loadScript('https://unpkg.com/emmet-monaco-es/dist/emmet-monaco.min.js');
+    if (window.emmetMonaco) {
+      emmetMonaco.emmetHTML(monaco);
+      emmetMonaco.emmetCSS(monaco);
+      emmetMonaco.emmetJSX(monaco);
+      loaded = true;
+    }
+  } catch (e) {
+    console.warn('Emmet load failed:', e.message);
+  }
+}

public/js/keybindings.js

@@ -0,0 +1,109 @@
+import { getPref, setPref } from './preferences.js';
+import { getActiveEditor, setOnTabSwitch, setOnModeChange } from './editors.js';
+
+let currentMode = 'default'; // 'default' | 'vim' | 'emacs'
+let activeAdapter = null;    // vim or emacs adapter instance
+let vimLoaded = false;
+let emacsLoaded = false;
+
+const statusBar = () => document.getElementById('vim-status-bar');
+
+function loadScript(src) {
+  return new Promise((resolve, reject) => {
+    if (document.querySelector(`script[src="${src}"]`)) { resolve(); return; }
+    const savedDefine = window.define;
+    window.define = undefined;
+    const s = document.createElement('script');
+    s.src = src;
+    s.onload = () => { window.define = savedDefine; resolve(); };
+    s.onerror = () => { window.define = savedDefine; reject(new Error(`Failed to load ${src}`)); };
+    document.head.appendChild(s);
+  });
+}
+
+async function ensureVim() {
+  if (vimLoaded) return;
+  window.monaco = monaco;
+  await loadScript('https://unpkg.com/monaco-vim@0.4.2/dist/monaco-vim.js');
+  vimLoaded = true;
+}
+
+async function ensureEmacs() {
+  if (emacsLoaded) return;
+  window.monaco = monaco;
+  await loadScript('https://unpkg.com/monaco-emacs/dist/monaco-emacs.js');
+  emacsLoaded = true;
+}
+
+function disposeAdapter() {
+  if (activeAdapter) {
+    activeAdapter.dispose();
+    activeAdapter = null;
+  }
+  const bar = statusBar();
+  if (bar) {
+    bar.style.display = 'none';
+    bar.textContent = '';
+  }
+}
+
+async function attachToEditor(editor) {
+  if (!editor) return;
+  disposeAdapter();
+
+  if (currentMode === 'vim') {
+    await ensureVim();
+    const bar = statusBar();
+    if (bar) bar.style.display = 'block';
+    activeAdapter = MonacoVim.initVimMode(editor, bar);
+  } else if (currentMode === 'emacs') {
+    await ensureEmacs();
+    const EmacsExtension = MonacoEmacs.EmacsExtension;
+    activeAdapter = new EmacsExtension(editor);
+    activeAdapter.start();
+  }
+}
+
+export async function setKeybindingMode(mode) {
+  disposeAdapter();
+  currentMode = mode;
+  setPref('keybindings', mode);
+
+  if (mode === 'default') return;
+
+  const editor = getActiveEditor();
+  if (editor) await attachToEditor(editor);
+}
+
+export function initKeybindings() {
+  currentMode = getPref('keybindings') || 'default';
+
+  const select = document.getElementById('keybinding-mode');
+  if (select) {
+    select.value = currentMode;
+    select.addEventListener('change', (e) => setKeybindingMode(e.target.value));
+  }
+
+  // Reattach on tab switch
+  setOnTabSwitch((_tabId, editor) => {
+    if (currentMode !== 'default' && editor) {
+      attachToEditor(editor);
+    }
+  });
+
+  // Reattach on mode change
+  setOnModeChange(() => {
+    if (currentMode !== 'default') {
+      setTimeout(() => {
+        const editor = getActiveEditor();
+        if (editor) attachToEditor(editor);
+      }, 50);
+    }
+  });
+
+  // Initial attach if non-default
+  if (currentMode !== 'default') {
+    const editor = getActiveEditor();
+    if (editor) attachToEditor(editor);
+  }
+}

public/js/preferences.js

@@ -0,0 +1,22 @@
+const PREFIX = 'fiddle_';
+
+const DEFAULTS = {
+  autoRun: true,
+  layout: 'default',
+  keybindings: 'default',
+  panelSizes: null,
+};
+
+export function getPref(key) {
+  const raw = localStorage.getItem(PREFIX + key);
+  if (raw === null) return DEFAULTS[key] ?? null;
+  try { return JSON.parse(raw); } catch { return raw; }
+}
+
+export function setPref(key, value) {
+  localStorage.setItem(PREFIX + key, JSON.stringify(value));
+}
+
+export function removePref(key) {
+  localStorage.removeItem(PREFIX + key);
+}

public/js/resizer.js

@@ -0,0 +1,91 @@
+import { getPref, setPref } from './preferences.js';
+import { relayoutEditors } from './editors.js';
+
+let grid = null;
+let colDivider = null;
+let rowDivider = null;
+let dragging = null; // 'col' | 'row' | null
+
+export function initResizer() {
+  grid = document.querySelector('.grid');
+  colDivider = document.getElementById('divider-col');
+  rowDivider = document.getElementById('divider-row');
+
+  if (!grid || !colDivider || !rowDivider) return;
+
+  // Restore saved sizes
+  const saved = getPref('panelSizes');
+  if (saved) applySizes(saved);
+
+  // Column divider (horizontal drag)
+  colDivider.addEventListener('mousedown', (e) => startDrag(e, 'col'));
+  colDivider.addEventListener('dblclick', () => resetSizes());
+
+  // Row divider (vertical drag)
+  rowDivider.addEventListener('mousedown', (e) => startDrag(e, 'row'));
+  rowDivider.addEventListener('dblclick', () => resetSizes());
+
+  document.addEventListener('mousemove', onMouseMove);
+  document.addEventListener('mouseup', onMouseUp);
+}
+
+function startDrag(e, type) {
+  e.preventDefault();
+  dragging = type;
+  document.body.classList.add('resizing');
+}
+
+function onMouseMove(e) {
+  if (!dragging) return;
+
+  const rect = grid.getBoundingClientRect();
+
+  if (dragging === 'col') {
+    const x = e.clientX - rect.left;
+    const total = rect.width;
+    const pct = Math.max(0.15, Math.min(0.85, x / total));
+    const left = pct;
+    const right = 1 - pct;
+    grid.style.gridTemplateColumns = `${left}fr 4px ${right}fr`;
+  } else if (dragging === 'row') {
+    const y = e.clientY - rect.top;
+    const total = rect.height;
+    const pct = Math.max(0.15, Math.min(0.85, y / total));
+    const top = pct;
+    const bottom = 1 - pct;
+    grid.style.gridTemplateRows = `${top}fr 4px ${bottom}fr`;
+  }
+
+  relayoutEditors();
+}
+
+function onMouseUp() {
+  if (!dragging) return;
+  dragging = null;
+  document.body.classList.remove('resizing');
+
+  // Persist current sizes
+  const sizes = {
+    cols: grid.style.gridTemplateColumns || null,
+    rows: grid.style.gridTemplateRows || null,
+  };
+  setPref('panelSizes', sizes);
+  relayoutEditors();
+}
+
+function applySizes(sizes) {
+  if (sizes.cols) grid.style.gridTemplateColumns = sizes.cols;
+  if (sizes.rows) grid.style.gridTemplateRows = sizes.rows;
+}
+
+export function resetSizes() {
+  grid.style.gridTemplateColumns = '';
+  grid.style.gridTemplateRows = '';
+  setPref('panelSizes', null);
+  relayoutEditors();
+}
+
+export function clearInlineSizes() {
+  grid.style.gridTemplateColumns = '';
+  grid.style.gridTemplateRows = '';
+}