Tweaked some things.

gulpfile.js

@@ -3,6 +3,7 @@ const pug = require('gulp-pug')
 const sass = require('gulp-sass')(require('sass'))
 const bs = require('browser-sync').create()
 const fs = require('fs')
+const helper = require('./theme/helper.js');
 
 function css () {
   return src('./theme/styles.scss')
@@ -14,7 +15,7 @@ function html () {
   const resume = JSON.parse(fs.readFileSync('./resume.json', 'utf-8'))
 
   return src('./theme/template.pug')
-    .pipe(pug({ data: { resume } }))
+    .pipe(pug({ data: { resume, helper } }))
     .pipe(dest('./public'))
 }
 

index.js

@@ -1,8 +1,10 @@
 const pug = require('pug');
 const path = require('path');
+const helper = require('./theme/helper')
 
 const render = (resume) => pug.renderFile(path.join(__dirname, 'theme', 'template.pug'),{
-    resume
+    resume,
+    helper
 })
 
 module.exports = {

package.json

@@ -4,7 +4,7 @@
   "description": "",
   "main": "index.js",
   "scripts": {
-    "dev": "resume serve --theme .",
+    "dev": "gulp",
     "resume": "resume",
     "build": "mkdir -p out && resume export out/resume.pdf && resume export out/resume.html"
   },

theme/helper.js

@@ -0,0 +1,28 @@
+const validArray = (array) => array !== undefined && array.length > 0;
+
+const formatdate = (date) => {
+  const monthNames = [
+    "January",
+    "February",
+    "March",
+    "April",
+    "May",
+    "June",
+    "July",
+    "August",
+    "September",
+    "October",
+    "November",
+    "December",
+  ];
+  const monthIndex = date.getMonth();
+  const year = date.getFullYear();
+
+  return `${monthNames[monthIndex]} ${year}`;
+}
+
+
+module.exports = {
+  validArray,
+  formatdate
+};

theme/pug/test.pug

@@ -0,0 +1 @@
+h1=helper.formatdate(new Date('2020-01-02'))

theme/styles.css

@@ -0,0 +1,3 @@
+.foo {
+  background-color: black;
+}

theme/styles.scss

@@ -1 +1,5 @@
-@charset "UTF-8";
+@charset "UTF-8";
+
+.foo{
+    background-color: black;
+}

theme/template.pug

@@ -4,5 +4,6 @@ html(lang="en")
         meta(charset="utf-8")
         style
             include styles.css 
-        title=`Resume ${resume.basics.name}`
+        title=`${resume.basics.name} - Resume`
-    body
+    body
+        include pug/test