Add npm install reminder on crash

CHANGELOG.md

@@ -1,3 +1,9 @@
+# Unreleased
+
+New features:
+
+- [Add npm install reminder when prototype crashes](https://github.com/alphagov/govuk-prototype-kit/pull/598)
+
 # 8.1.0
 
 New features:

gulp/nodemon.js

@@ -8,23 +8,35 @@ const fs = require('fs')
 const path = require('path')
 
 const gulp = require('gulp')
+const gutil = require('gulp-util')
 const nodemon = require('gulp-nodemon')
 
 const config = require('./config.json')
 
+// Warn about npm install on crash
+const onCrash = () => {
+  gutil.log(gutil.colors.cyan('[nodemon] For missing modules try running `npm install`'))
+}
+
+// Remove .port.tmp if it exists
+const onQuit = () => {
+  try {
+    fs.unlinkSync(path.join(__dirname, '/../.port.tmp'))
+  } catch (e) {}
+
+  process.exit(0)
+}
+
 gulp.task('server', function () {
   nodemon({
     watch: ['.env', '**/*.js', '**/*.json'],
     script: 'server.js',
-    ignore: [config.paths.public + '*',
+    ignore: [
+      config.paths.public + '*',
       config.paths.assets + '*',
-      config.paths.nodeModules + '*']
-  }).on('quit', function () {
-    // remove .port.tmp if it exists
-    try {
-      fs.unlinkSync(path.join(__dirname, '/../.port.tmp'))
-    } catch (e) {}
-
-    process.exit(0)
+      config.paths.nodeModules + '*'
+    ]
   })
+    .on('crash', onCrash)
+    .on('quit', onQuit)
 })