diff --git a/FilterEngine.js.html b/FilterEngine.js.html
new file mode 100644
index 0000000..b97680a
--- /dev/null
+++ b/FilterEngine.js.html
@@ -0,0 +1,141 @@
+<script>
+/**
+ * FilterEngine.js.html — Filter logic methods extracted from JavaScript.html
+ *
+ * Part of #129 Phase 1 (PR4/7): IIFE-wrapped domain separation.
+ * These methods handle tag/course/teacher filtering, persisted filter
+ * restoration, and schedule data filtering by predicates.
+ *
+ * Load order: after JavaScript.html + DataCollection.js (which provides
+ * App.getAllTags), before App.init() trigger.
+ *
+ * Dependencies: DataCollection.js (App.getAllTags), AppElements (filter* DOM),
+ * localStorage (persisted filters)
+ */
+(function(App) {
+
+  // --- Filter UI methods ---
+
+  App.loadAndApplyPersistedFilters = function() {
+    const persistedTagsJSON = localStorage.getItem('activeTagFilters');
+    if (persistedTagsJSON) {
+      try {
+        const persistedTags = JSON.parse(persistedTagsJSON);
+        const allCurrentTags = new Set(App.getAllTags());
+
+        const validPersistedTags = persistedTags.filter(tag => allCurrentTags.has(tag));
+
+        App.activeFilters = validPersistedTags.map(tag => ({ type: 'tag', value: tag }));
+
+        if (App.tagFilterTagify) {
+          App.tagFilterTagify.loadOriginalValues(validPersistedTags);
+        }
+
+        if (persistedTags.length !== validPersistedTags.length) {
+          localStorage.setItem('activeTagFilters', JSON.stringify(validPersistedTags));
+        }
+      } catch (e) {
+        console.error("Failed to parse persisted tag filters:", e);
+        localStorage.removeItem('activeTagFilters');
+        App.activeFilters = [];
+      }
+    } else {
+      App.activeFilters = [];
+    }
+    App.ui.updateClearFilterButtonVisibility();
+    App.ui.updateAdvancedFilterButtonState();
+    App.ui.updateClearAllFiltersButtonVisibility();
+  };
+
+  App.toggleAllFilterCheckboxes = function(shouldBeChecked) {
+    AppElements.filterCourseList.querySelectorAll('input[type="checkbox"]').forEach(cb => {
+      cb.checked = shouldBeChecked;
+    });
+  };
+
+  App.applyFilters = function() {
+    const filterType = AppElements.filterTypeSelector.querySelector('input[name="filterType"]:checked').value;
+    const selectedItems = Array.from(AppElements.filterCourseList.querySelectorAll('input[type="checkbox"]:checked')).map(cb => cb.value);
+
+    const tagFilters = App.activeFilters.filter(f => f.type === 'tag');
+    const newAdvancedFilters = selectedItems.map(item => ({ type: filterType, value: item }));
+    App.activeFilters = [...tagFilters, ...newAdvancedFilters];
+
+    App.ui.renderScheduleTable();
+    App.ui.updateAdvancedFilterButtonState();
+    App.ui.updateClearAllFiltersButtonVisibility();
+    AppElements.filterModal.style.display = 'none';
+  };
+
+  App.clearAdvancedFilters = function() {
+    App.activeFilters = App.activeFilters.filter(f => f.type === 'tag');
+    App.modals.populateFilterModal();
+    App.ui.renderScheduleTable();
+    App.ui.updateAdvancedFilterButtonState();
+    App.ui.updateClearAllFiltersButtonVisibility();
+  };
+
+  App.clearAllFilters = function() {
+    App.activeFilters = [];
+    localStorage.removeItem('activeTagFilters');
+    if (App.tagFilterTagify) {
+      App.tagFilterTagify.removeAllTags();
+    }
+    App.modals.populateFilterModal();
+    App.ui.renderScheduleTable();
+    App.ui.updateAdvancedFilterButtonState();
+    App.ui.updateClearFilterButtonVisibility();
+    App.ui.updateClearAllFiltersButtonVisibility();
+  };
+
+  // --- Data filtering methods ---
+
+  App._filterScheduleData = function(data, filterPredicate) {
+    const filteredData = {};
+    for (const classroom in data) {
+      const dayData = data[classroom];
+      const newDayData = {};
+      let classroomHasCourses = false;
+      for (const day in dayData) {
+        const filteredCourses = dayData[day].filter(filterPredicate);
+        if (filteredCourses.length > 0) {
+          newDayData[day] = filteredCourses;
+          classroomHasCourses = true;
+        }
+      }
+      if (classroomHasCourses) {
+        filteredData[classroom] = newDayData;
+      }
+    }
+    return filteredData;
+  };
+
+  App.filterDataByTags = function(data) {
+    const tagFilters = new Set(App.activeFilters.filter(f => f.type === 'tag').map(f => f.value));
+    if (tagFilters.size === 0) {
+      return data;
+    }
+    return App._filterScheduleData(data, course =>
+      course.tags && course.tags.some(d => tagFilters.has(d))
+    );
+  };
+
+  App.filterDataByActiveFilters = function(data) {
+    const nameFilters = new Set(App.activeFilters.filter(f => f.type === 'name').map(f => f.value));
+    const tagFilters = new Set(App.activeFilters.filter(f => f.type === 'tag').map(f => f.value));
+    const teacherFilters = new Set(App.activeFilters.filter(f => f.type === 'teacher').map(f => f.value));
+
+    if (nameFilters.size === 0 && tagFilters.size === 0 && teacherFilters.size === 0) {
+      return data;
+    }
+
+    return App._filterScheduleData(data, course => {
+      const nameMatch = nameFilters.size === 0 || nameFilters.has(course.name);
+      const tagMatch = tagFilters.size === 0 || (course.tags && course.tags.some(d => tagFilters.has(d)));
+      const teacherMatch = teacherFilters.size === 0 || teacherFilters.has(course.teacher);
+      return nameMatch && tagMatch && teacherMatch;
+    });
+  };
+
+})(App);
+</script>
diff --git a/Index.html b/Index.html
index c9a2cbd..ebf4441 100644
--- a/Index.html
+++ b/Index.html
@@ -476,6 +476,7 @@ <h2 class="text-2xl font-bold mb-6 text-center text-purple-800">PDF 下載選項
     <?!= HtmlService.createHtmlOutputFromFile('UtilityFunctions.js').getContent(); ?>
     <?!= HtmlService.createHtmlOutputFromFile('LockManager.js').getContent(); ?>
     <?!= HtmlService.createHtmlOutputFromFile('DataCollection.js').getContent(); ?>
+    <?!= HtmlService.createHtmlOutputFromFile('FilterEngine.js').getContent(); ?>
     <script>App.init();</script>
 </body>
 </html>
diff --git a/JavaScript.html b/JavaScript.html
index b2067f5..f57e48d 100644
--- a/JavaScript.html
+++ b/JavaScript.html
@@ -398,37 +398,8 @@
                 }
             },
 
-            // --- FILTER LOGIC ---
-            loadAndApplyPersistedFilters: function () {
-                const persistedTagsJSON = localStorage.getItem('activeTagFilters');
-                if (persistedTagsJSON) {
-                    try {
-                        const persistedTags = JSON.parse(persistedTagsJSON);
-                        const allCurrentTags = new Set(this.getAllTags());
-
-                        const validPersistedTags = persistedTags.filter(tag => allCurrentTags.has(tag));
-
-                        this.activeFilters = validPersistedTags.map(tag => ({ type: 'tag', value: tag }));
-
-                        if (this.tagFilterTagify) {
-                            this.tagFilterTagify.loadOriginalValues(validPersistedTags);
-                        }
-
-                        if (persistedTags.length !== validPersistedTags.length) {
-                            localStorage.setItem('activeTagFilters', JSON.stringify(validPersistedTags));
-                        }
-                    } catch (e) {
-                        console.error("Failed to parse persisted tag filters:", e);
-                        localStorage.removeItem('activeTagFilters');
-                        this.activeFilters = [];
-                    }
-                } else {
-                    this.activeFilters = [];
-                }
-                this.ui.updateClearFilterButtonVisibility();
-                this.ui.updateAdvancedFilterButtonState();
-                this.ui.updateClearAllFiltersButtonVisibility();
-            },
+            // loadAndApplyPersistedFilters, toggleAllFilterCheckboxes, applyFilters — moved to FilterEngine.js.html (Phase 1 PR4)
+            // clearAdvancedFilters, clearAllFilters — moved to FilterEngine.js.html (Phase 1 PR4)
 
             applyTagFilters: async function () {
                 if (!this.tagFilterTagify) return;
@@ -460,47 +431,6 @@
                 this.ui.updateClearAllFiltersButtonVisibility();
             },
 
-            toggleAllFilterCheckboxes: function (shouldBeChecked) {
-                AppElements.filterCourseList.querySelectorAll('input[type="checkbox"]').forEach(cb => {
-                    cb.checked = shouldBeChecked;
-                });
-            },
-
-            applyFilters: function () {
-                const filterType = AppElements.filterTypeSelector.querySelector('input[name="filterType"]:checked').value;
-                const selectedItems = Array.from(AppElements.filterCourseList.querySelectorAll('input[type="checkbox"]:checked')).map(cb => cb.value);
-
-                const tagFilters = this.activeFilters.filter(f => f.type === 'tag');
-                const newAdvancedFilters = selectedItems.map(item => ({ type: filterType, value: item }));
-                this.activeFilters = [...tagFilters, ...newAdvancedFilters];
-
-                this.ui.renderScheduleTable();
-                this.ui.updateAdvancedFilterButtonState();
-                this.ui.updateClearAllFiltersButtonVisibility();
-                AppElements.filterModal.style.display = 'none';
-            },
-
-            clearAdvancedFilters: function () {
-                this.activeFilters = this.activeFilters.filter(f => f.type === 'tag');
-                this.modals.populateFilterModal();
-                this.ui.renderScheduleTable();
-                this.ui.updateAdvancedFilterButtonState();
-                this.ui.updateClearAllFiltersButtonVisibility();
-            },
-
-            clearAllFilters: function () {
-                this.activeFilters = [];
-                localStorage.removeItem('activeTagFilters');
-                if (this.tagFilterTagify) {
-                    this.tagFilterTagify.removeAllTags();
-                }
-                this.modals.populateFilterModal();
-                this.ui.renderScheduleTable();
-                this.ui.updateAdvancedFilterButtonState();
-                this.ui.updateClearFilterButtonVisibility();
-                this.ui.updateClearAllFiltersButtonVisibility();
-            },
-
             // --- API COMMUNICATION ---
             loadVersions: async function () {
                 const select = AppElements.versionHistorySelect;
@@ -733,52 +663,7 @@
 
             // formatTimestampForFilename — moved to UtilityFunctions.js.html (Phase 1 PR1)
 
-            _filterScheduleData: function (data, filterPredicate) {
-                const filteredData = {};
-                for (const classroom in data) {
-                    const dayData = data[classroom];
-                    const newDayData = {};
-                    let classroomHasCourses = false;
-                    for (const day in dayData) {
-                        const filteredCourses = dayData[day].filter(filterPredicate);
-                        if (filteredCourses.length > 0) {
-                            newDayData[day] = filteredCourses;
-                            classroomHasCourses = true;
-                        }
-                    }
-                    if (classroomHasCourses) {
-                        filteredData[classroom] = newDayData;
-                    }
-                }
-                return filteredData;
-            },
-
-            filterDataByTags: function (data) {
-                const tagFilters = new Set(this.activeFilters.filter(f => f.type === 'tag').map(f => f.value));
-                if (tagFilters.size === 0) {
-                    return data;
-                }
-                return this._filterScheduleData(data, course =>
-                    course.tags && course.tags.some(d => tagFilters.has(d))
-                );
-            },
-
-            filterDataByActiveFilters: function (data) {
-                const nameFilters = new Set(this.activeFilters.filter(f => f.type === 'name').map(f => f.value));
-                const tagFilters = new Set(this.activeFilters.filter(f => f.type === 'tag').map(f => f.value));
-                const teacherFilters = new Set(this.activeFilters.filter(f => f.type === 'teacher').map(f => f.value));
-
-                if (nameFilters.size === 0 && tagFilters.size === 0 && teacherFilters.size === 0) {
-                    return data;
-                }
-
-                return this._filterScheduleData(data, course => {
-                    const nameMatch = nameFilters.size === 0 || nameFilters.has(course.name);
-                    const tagMatch = tagFilters.size === 0 || (course.tags && course.tags.some(d => tagFilters.has(d)));
-                    const teacherMatch = teacherFilters.size === 0 || teacherFilters.has(course.teacher);
-                    return nameMatch && tagMatch && teacherMatch;
-                });
-            },
+            // _filterScheduleData, filterDataByTags, filterDataByActiveFilters — moved to FilterEngine.js.html (Phase 1 PR4)
 
             // _forEachCourse, countOccurrences, updateAllOccurrences — moved to DataCollection.js.html (Phase 1 PR3)
 
diff --git a/tests/unit/appWiringContracts.test.js b/tests/unit/appWiringContracts.test.js
index f2c09e5..b8017ad 100644
--- a/tests/unit/appWiringContracts.test.js
+++ b/tests/unit/appWiringContracts.test.js
@@ -62,14 +62,10 @@ const privateMethods = extractPrivateMethods(jsHtmlSource);
 const EXTRACTED_TO_LIB = new Set([
   // stateHelpers.js
   'handleEditClassroom', 'saveDataToServer',
-  // frontendUtils.js
-  'filterDataByTags', 'filterDataByActiveFilters',
   // interactionHelpers.js (handleDrop → applyDrop)
   'handleDrop',
   // appLifecycleHelpers.js (new — this wave)
   'loadInitialSchedules', 'loadSchedule', 'canManageCurrentScheduleSettings',
-  'loadAndApplyPersistedFilters', 'applyFilters', 'clearAdvancedFilters',
-  'clearAllFilters',
   'saveSchedulesToLocal',
 ]);
 
@@ -85,7 +81,6 @@ const NOT_EXTRACTABLE = new Set([
   'handleScheduleListClick',      // DOM event delegation + ServerApi + modals
   'handleScheduleSelectChange',   // DOM event + modal confirm + state (aggregateScheduleData already extracted)
   'applyTagFilters',              // Tagify instance + modal confirm + DOM
-  'toggleAllFilterCheckboxes',    // DOM querySelectorAll
   'loadVersions',                 // DOM + ServerApi
   'handleLoadVersion',            // DOM + ServerApi + state
   'saveDataToLocal',              // localStorage + Tagify + DOM (core sync logic extracted as processServerLoadResult)
@@ -99,7 +94,7 @@ const NOT_EXTRACTABLE = new Set([
  * These are tested indirectly through their public callers.
  */
 const PRIVATE_HELPERS = new Set([
-  '_filterScheduleData',
+  // _filterScheduleData — moved to FilterEngine.js.html (Phase 1 PR4)
 ]);
 
 /**
@@ -121,6 +116,12 @@ const IIFE_EXTRACTED = new Set([
   'checkTimeConflict',
   // DataCollection.js.html (PR3) — private helpers also IIFE-extracted
   '_forEachCourse', '_collectFromScheduleData', '_collectFromAllCourses',
+  // FilterEngine.js.html (PR4)
+  'loadAndApplyPersistedFilters', 'toggleAllFilterCheckboxes', 'applyFilters',
+  'clearAdvancedFilters', 'clearAllFilters',
+  'filterDataByTags', 'filterDataByActiveFilters',
+  // FilterEngine.js.html (PR4) — private helpers also IIFE-extracted
+  '_filterScheduleData',
 ]);
 
 // ─── Tests ─────────────────────────────────────────────────────────────────
@@ -133,8 +134,8 @@ describe('JavaScript.html App method wiring contracts (#116)', () => {
   it('should have expected total App method count', () => {
     // All public methods (excluding underscore-prefixed private helpers)
     const publicMethods = appMethods.filter(m => !m.startsWith('_'));
-    // 48 original - 7 PR1 - 4 PR2 public - 11 PR3 public = 26 remaining in JavaScript.html
-    expect(publicMethods.length).toBe(26);
+    // 48 original - 7 PR1 - 4 PR2 public - 11 PR3 public - 7 PR4 public = 19 remaining in JavaScript.html
+    expect(publicMethods.length).toBe(19);
   });
 
   it('every public App method should be classified (extracted OR not-extractable)', () => {
diff --git a/tests/unit/syncMethodsWiring.test.js b/tests/unit/syncMethodsWiring.test.js
index cd856ba..b13a7ab 100644
--- a/tests/unit/syncMethodsWiring.test.js
+++ b/tests/unit/syncMethodsWiring.test.js
@@ -25,6 +25,12 @@ const lockManagerSource = readFileSync(
   'utf-8'
 );
 
+// FilterEngine methods moved to separate IIFE module (Phase 1 PR4)
+const filterEngineSource = readFileSync(
+  resolve(import.meta.dirname, '../../FilterEngine.js.html'),
+  'utf-8'
+);
+
 // ─── Helpers (shared pattern from Wave 2) ────────────────────────────────
 
 /**
@@ -107,19 +113,19 @@ const SYNC_METHOD_WIRING = [
     'input\\[type=.checkbox.\\]',
   ]],
   ['clearAdvancedFilters', [
-    'this\\.activeFilters',
-    'this\\.modals\\.populateFilterModal',
-    'this\\.ui\\.renderScheduleTable',
-    'this\\.ui\\.updateAdvancedFilterButtonState',
-    'this\\.ui\\.updateClearAllFiltersButtonVisibility',
+    'App\\.activeFilters',
+    'App\\.modals\\.populateFilterModal',
+    'App\\.ui\\.renderScheduleTable',
+    'App\\.ui\\.updateAdvancedFilterButtonState',
+    'App\\.ui\\.updateClearAllFiltersButtonVisibility',
   ]],
   ['clearAllFilters', [
-    'this\\.activeFilters',
+    'App\\.activeFilters',
     'localStorage\\.removeItem',
-    'this\\.tagFilterTagify',
+    'App\\.tagFilterTagify',
     'removeAllTags',
-    'this\\.modals\\.populateFilterModal',
-    'this\\.ui\\.renderScheduleTable',
+    'App\\.modals\\.populateFilterModal',
+    'App\\.ui\\.renderScheduleTable',
   ]],
   ['_getLocks', [
     'localStorage\\.getItem',
@@ -169,9 +175,10 @@ describe('Sync App Methods — Wiring Smoke Tests (Static Analysis)', () => {
   // ─── 1. Method existence ──────────────────────────────────────────────
 
   describe('all sync methods exist in JavaScript.html or IIFE modules', () => {
-    // Non-lock methods from JavaScript.html
+    // Non-lock, non-filter methods from JavaScript.html
     const jsHtmlMethods = SYNC_METHOD_WIRING.filter(([n]) =>
-      !['_getLocks', '_saveLocks', 'releaseCurrentLock', 'refreshLockHeartbeat'].includes(n)
+      !['_getLocks', '_saveLocks', 'releaseCurrentLock', 'refreshLockHeartbeat',
+       'toggleAllFilterCheckboxes', 'clearAdvancedFilters', 'clearAllFilters'].includes(n)
     );
     it.each(jsHtmlMethods)(
       '%s is declared in JavaScript.html',
@@ -193,6 +200,18 @@ describe('Sync App Methods — Wiring Smoke Tests (Static Analysis)', () => {
         expect(body).not.toBeNull();
       }
     );
+
+    // Filter methods from FilterEngine.js.html (Phase 1 PR4)
+    const filterMethods = SYNC_METHOD_WIRING.filter(([n]) =>
+      ['toggleAllFilterCheckboxes', 'clearAdvancedFilters', 'clearAllFilters'].includes(n)
+    );
+    it.each(filterMethods)(
+      '%s is declared in FilterEngine.js.html',
+      (methodName, _patterns) => {
+        const body = extractMethodBody(filterEngineSource, methodName);
+        expect(body).not.toBeNull();
+      }
+    );
   });
 
   // ─── 2. Wiring correctness ────────────────────────────────────────────
@@ -237,11 +256,12 @@ describe('Sync App Methods — Wiring Smoke Tests (Static Analysis)', () => {
   });
 
   describe('filter methods — DOM state management', () => {
-    const filterMethods = ['toggleAllFilterCheckboxes', 'clearAdvancedFilters', 'clearAllFilters'];
+    const filterMethodNames = ['toggleAllFilterCheckboxes', 'clearAdvancedFilters', 'clearAllFilters'];
 
-    for (const methodName of filterMethods) {
+    for (const methodName of filterMethodNames) {
       const [, patterns] = SYNC_METHOD_WIRING.find(([n]) => n === methodName);
-      const body = extractMethodBody(jsHtmlSource, methodName);
+      // Filter methods now in FilterEngine.js.html
+      const body = extractMethodBody(filterEngineSource, methodName);
 
       describe(methodName, () => {
         it.each(patterns)(