diff --git a/build/build.js b/build/build.js
index 360e0b4c8c..8dbb32ced1 100644
--- a/build/build.js
+++ b/build/build.js
@@ -11,10 +11,10 @@ const colors = require('colors-cli/toxic');
 const renderer = new marked.Renderer();
 renderer.heading = (text, level) => {
   if (/[\u4E00-\u9FA5]/i.test(text)) {
-    return '<h' + level + ' id="' + text.toLowerCase() + '">' + text + '</h' + level + '>';
+    return `<h${level} id="${text.toLowerCase()}">${text}</h${level}>`;
   } else {
-    var escapedText = text.toLowerCase().replace(/[^\w]+/g, '-');
-    return '<h' + level + ' id="' + escapedText + '">' + text + '</h' + level + '>';
+    const escapedText = text.toLowerCase().replace(/[^\w]+/g, '-');
+    return `<h${level} id="${escapedText}">${text}</h${level}>`;
   }
 }