diff --git a/lib/extend/injector.js b/lib/extend/injector.js
index 2cab5514a5..74689d3202 100644
--- a/lib/extend/injector.js
+++ b/lib/extend/injector.js
@@ -28,6 +28,10 @@ class Injector {
     return arr.join('');
   }
 
+  getSize(entry) {
+    return this.cache.apply(`${entry}-size`, Object.keys(this.store[entry]).length);
+  }
+
   register(entry, value, to = 'default') {
     if (!entry) throw new TypeError('entry is required');
     if (typeof value === 'function') value = value();
@@ -38,41 +42,58 @@ class Injector {
     entryMap[to] = valueSet;
   }
 
-  exec(data, locals = { page: {} }) {
+  _getPageType(pageLocals) {
     let currentType = 'default';
-    const { page } = locals;
+    if (pageLocals.__index) currentType = 'home';
+    if (pageLocals.__post) currentType = 'post';
+    if (pageLocals.__page) currentType = 'page';
+    if (pageLocals.archive) currentType = 'archive';
+    if (pageLocals.category) currentType = 'category';
+    if (pageLocals.tag) currentType = 'tag';
+    if (pageLocals.layout) currentType = pageLocals.layout;
+
+    return currentType;
+  }
 
-    if (page.__index) currentType = 'home';
-    if (page.__post) currentType = 'post';
-    if (page.__page) currentType = 'page';
-    if (page.archive) currentType = 'archive';
-    if (page.category) currentType = 'category';
-    if (page.tag) currentType = 'tag';
-    if (page.layout) currentType = page.layout;
+  _injector(input, pattern, flag, isBegin = true, currentType) {
+    if (input.includes(`hexo injector ${flag}`)) return input;
 
-    const injector = (data, pattern, flag, isBegin = true) => {
-      if (data.includes(`hexo injector ${flag}`)) return data;
+    const code = this.cache.apply(`${flag}-${currentType}-code`, () => {
+      const content = currentType === 'default' ? this.getText(flag, 'default') : this.getText(flag, currentType) + this.getText(flag, 'default');
 
-      const code = this.cache.apply(`${flag}-${currentType}-code`, () => {
-        const content = currentType === 'default' ? this.getText(flag, 'default') : this.getText(flag, currentType) + this.getText(flag, 'default');
+      if (!content.length) return '';
+      return '<!-- hexo injector ' + flag + ' start -->' + content + '<!-- hexo injector ' + flag + ' end -->';
+    });
 
-        if (!content.length) return '';
-        return '<!-- hexo injector ' + flag + ' start -->' + content + '<!-- hexo injector ' + flag + ' end -->';
-      });
+    // avoid unnecessary replace() for better performance
+    if (!code.length) return input;
 
-      // avoid unnecessary replace() for better performance
-      if (!code.length) return data;
-      return data.replace(pattern, str => { return isBegin ? str + code : code + str; });
-    };
+    return input.replace(pattern, str => { return isBegin ? str + code : code + str; });
+  }
 
-    // Inject head_begin
-    data = injector(data, /<head.*?>/, 'head_begin', true);
-    // Inject head_end
-    data = injector(data, '</head>', 'head_end', false);
-    // Inject body_begin
-    data = injector(data, /<body.*?>/, 'body_begin', true);
-    // Inject body_end
-    data = injector(data, '</body>', 'body_end', false);
+  exec(data, locals = { page: {} }) {
+    const { page } = locals;
+    const currentType = this._getPageType(page);
+
+    if (this.getSize('head_begin') !== 0) {
+      // Inject head_begin
+      data = this._injector(data, /<head.*?>/, 'head_begin', true, currentType);
+    }
+
+    if (this.getSize('head_end') !== 0) {
+      // Inject head_end
+      data = this._injector(data, '</head>', 'head_end', false, currentType);
+    }
+
+    if (this.getSize('body_begin') !== 0) {
+      // Inject body_begin
+      data = this._injector(data, /<body.*?>/, 'body_begin', true, currentType);
+    }
+
+    if (this.getSize('body_end') !== 0) {
+      // Inject body_end
+      data = this._injector(data, '</body>', 'body_end', false, currentType);
+    }
 
     return data;
   }
diff --git a/test/scripts/extend/injector.js b/test/scripts/extend/injector.js
index 900c331f8f..08ffc8110c 100644
--- a/test/scripts/extend/injector.js
+++ b/test/scripts/extend/injector.js
@@ -94,6 +94,19 @@ describe('Injector', () => {
     i.getText('body_end').should.eql('');
   });
 
+  it('getSize()', () => {
+    const i = new Injector();
+    const str = '<script src="jquery.min.js"></script>';
+
+    i.register('head_end', str);
+    i.register('body_end', str);
+    i.register('body_end', str, 'home');
+
+    i.getSize('head_begin').should.eql(0);
+    i.getSize('head_end').should.eql(1);
+    i.getSize('body_end').should.eql(2);
+  });
+
   it('exec() - default', () => {
     const i = new Injector();
     const result = i.exec(content);