diff --git a/scripts/helpers/engine.js b/scripts/helpers/engine.js
index 6b2f703..13b1e7c 100644
--- a/scripts/helpers/engine.js
+++ b/scripts/helpers/engine.js
@@ -19,7 +19,9 @@ hexo.extend.helper.register('next_inject', function(point) {
 
 hexo.extend.helper.register('next_js', function(file, {
   pjax = false,
-  module = false
+  module = false,
+  async = false,
+  defer = !async
 } = {}) {
   const { next_version } = this;
   const { internal, custom_cdn_url } = this.theme.vendors;
@@ -32,18 +34,21 @@ hexo.extend.helper.register('next_js', function(file, {
     custom  : custom_cdn_url
   });
   const src = links[internal] || links.local;
-  return `<script ${pjax ? 'data-pjax ' : ''}${module ? 'type="module" ' : ''}src="${src}" defer></script>`;
+  return `<script ${pjax ? 'data-pjax ' : ''}${module ? 'type="module" ' : ''}src="${src}"${defer ? ' defer' : ''}${async ? ' async' : ''}></script>`;
 });
 
-hexo.extend.helper.register('next_vendors', function(name) {
+hexo.extend.helper.register('next_vendors', function(name, {
+  async = false,
+  defer = !async
+} = {}) {
   const { url, integrity } = this.theme.vendors[name];
   const type = url.endsWith('css') ? 'css' : 'js';
   if (type === 'css') {
     if (integrity) return `<link rel="stylesheet" href="${url}" integrity="${integrity}" crossorigin="anonymous">`;
     return `<link rel="stylesheet" href="${url}">`;
   }
-  if (integrity) return `<script src="${url}" integrity="${integrity}" crossorigin="anonymous" defer></script>`;
-  return `<script src="${url}" defer></script>`;
+  if (integrity) return `<script src="${url}" integrity="${integrity}" crossorigin="anonymous"${defer ? ' defer' : ''}${async ? ' async' : ''}></script>`;
+  return `<script src="${url}"${defer ? ' defer' : ''}${async ? ' async' : ''}></script>`;
 });
 
 hexo.extend.helper.register('next_data', function(name, ...data) {
diff --git a/test/helpers/engine.js b/test/helpers/engine.js
new file mode 100644
index 0000000..c66f008
--- /dev/null
+++ b/test/helpers/engine.js
@@ -0,0 +1,73 @@
+'use strict';
+
+const helpers = {};
+
+global.hexo = {
+  extend: {
+    helper: {
+      register(name, helper) {
+        helpers[name] = helper;
+      }
+    }
+  }
+};
+
+require('../../scripts/helpers/engine');
+delete global.hexo;
+
+describe('engine', () => {
+  const context = {
+    next_version: '8.28.0',
+    theme       : {
+      js     : 'js',
+      vendors: {
+        internal      : 'local',
+        custom_cdn_url: '',
+        library       : {
+          url: 'https://cdn.example.com/library.js'
+        },
+        secure_library: {
+          url      : 'https://cdn.example.com/secure.js',
+          integrity: 'sha256-example'
+        },
+        stylesheet: {
+          url: 'https://cdn.example.com/library.css'
+        }
+      }
+    },
+    url_for(path) {
+      return '/' + path;
+    }
+  };
+
+  const nextJs = helpers.next_js.bind(context);
+  const nextVendors = helpers.next_vendors.bind(context);
+
+  it('keeps defer as the default for NexT scripts', () => {
+    nextJs('main.js').should.eql('<script src="/js/main.js" defer></script>');
+  });
+
+  it('supports custom loading options for NexT scripts', () => {
+    nextJs('main.js', { defer: false }).should.eql('<script src="/js/main.js"></script>');
+    nextJs('main.js', { async: true }).should.eql('<script src="/js/main.js" async></script>');
+    nextJs('main.js', { defer: true, async: true }).should.eql('<script src="/js/main.js" defer async></script>');
+  });
+
+  it('preserves existing NexT script options', () => {
+    nextJs('main.js', { pjax: true, module: true }).should.eql('<script data-pjax type="module" src="/js/main.js" defer></script>');
+  });
+
+  it('keeps defer as the default for vendor scripts', () => {
+    nextVendors('library').should.eql('<script src="https://cdn.example.com/library.js" defer></script>');
+    nextVendors('secure_library').should.eql('<script src="https://cdn.example.com/secure.js" integrity="sha256-example" crossorigin="anonymous" defer></script>');
+  });
+
+  it('supports custom loading options for vendor scripts', () => {
+    nextVendors('library', { defer: false }).should.eql('<script src="https://cdn.example.com/library.js"></script>');
+    nextVendors('library', { async: true }).should.eql('<script src="https://cdn.example.com/library.js" async></script>');
+  });
+
+  it('does not apply script loading options to stylesheets', () => {
+    nextVendors('stylesheet', { async: true }).should.eql('<link rel="stylesheet" href="https://cdn.example.com/library.css">');
+  });
+});
diff --git a/test/helpers/index.js b/test/helpers/index.js
index 3ef5dde..9769bca 100644
--- a/test/helpers/index.js
+++ b/test/helpers/index.js
@@ -1,6 +1,7 @@
 'use strict';
 
 describe('Helpers', () => {
+  require('./engine');
   require('./font');
   require('./next-url');
 });