Prompt user to provide a new port if 4000 is already in use (#27)

* Prompt user to provide a new port if 4000 is already in use

* fixing lint errors

lib/detect-free-port.js

@@ -0,0 +1,23 @@
+'use strict'
+const co = require('co')
+const detect = require('detect-port')
+const chalk = require('chalk')
+const terminalUtils = require('./terminal-utils')
+
+module.exports = co.wrap(function * (DEFAULT_PORT) {
+  let port = yield detect(DEFAULT_PORT)
+
+  if (port === DEFAULT_PORT) {
+    return port
+  }
+
+  terminalUtils.clearConsole()
+
+  let question
+    = chalk.yellow(`Something is already running on port ${DEFAULT_PORT}.`)
+    + '\n\nWould you like to run the app on another port instead?'
+
+  let shouldChangePort = yield terminalUtils.prompt(question, true)
+
+  return shouldChangePort ? port : null
+})

lib/index.js

@@ -5,6 +5,7 @@ const merge = require('lodash.merge')
 const build = require('./build')
 const dev = require('./dev')
 const updateConfig = require('./update-config')
+const detectFreePort = require('./detect-free-port')
 
 module.exports = co.wrap(function * (options) {
   options.config = options.config === false
@@ -36,8 +37,14 @@ module.exports = co.wrap(function * (options) {
 
   process.env.NODE_ENV = isDev ? 'development' : 'production'
 
+  let port = yield detectFreePort(4000)
+
+  if (!port) {
+    return
+  }
+
   const buildOptions = merge(
-    {port: 4000},
+    {port},
     fileConfig,
     isDev ? devConfig : prodConfig,
     options

lib/terminal-utils.js

@@ -0,0 +1,43 @@
+'use strict'
+const rl = require('readline')
+
+const _ = module.exports = {}
+
+// Convention: "no" should be the conservative choice.
+// If you mistype the answer, we'll always take it as a "no".
+// You can control the behavior on <Enter> with `isYesDefault`.
+_.prompt = function (question, isYesDefault) {
+  if (typeof isYesDefault !== 'boolean') {
+    throw new Error('Provide explicit boolean isYesDefault as second argument.')
+  }
+  return new Promise(resolve => {
+    let rlInterface = rl.createInterface({
+      input: process.stdin,
+      output: process.stdout
+    })
+
+    let hint = isYesDefault === true ? '[Y/n]' : '[y/N]'
+    let message = question + ' ' + hint + '\n'
+
+    rlInterface.question(message, function (answer) {
+      rlInterface.close()
+
+      let useDefault = answer.trim().length === 0
+      if (useDefault) {
+        return resolve(isYesDefault)
+      }
+
+      let isYes = answer.match(/^(yes|y)$/i)
+      return resolve(isYes)
+    })
+  })
+}
+
+let isFirstClear = true
+_.clearConsole = function clearConsole() {
+  // On first run, clear completely so it doesn't show half screen on Windows.
+  // On next runs, use a different sequence that properly scrolls back.
+  process.stdout.write(isFirstClear ? '\x1bc' : '\x1b[2J\x1b[0f')
+  isFirstClear = false
+}
+

package.json

@@ -68,6 +68,7 @@
     "compression-webpack-plugin": "^0.3.1",
     "css-loader": "^0.25.0",
     "detect-installed": "^1.0.4",
+    "detect-port": "^1.0.1",
     "eslint": "^3.6.1",
     "eslint-config-egoist-vue": "^2.0.6",
     "eslint-loader": "^1.5.0",

yarn.lock

@@ -1626,7 +1626,7 @@ commander@^2.2.0, commander@^2.5.0, commander@^2.8.1, commander@^2.9.0, commande
   dependencies:
     graceful-readlink ">= 1.0.0"
 
-commander@2.8.x:
+commander@~2.8.1, commander@2.8.x:
   version "2.8.1"
   resolved "https://registry.yarnpkg.com/commander/-/commander-2.8.1.tgz#06be367febfda0c330aa1e2a072d3dc9762425d4"
   dependencies:
@@ -2126,6 +2126,12 @@ detect-installed@^1.0.4:
   dependencies:
     global-modules "^0.2.0"
 
+detect-port:
+  version "1.0.1"
+  resolved "https://registry.yarnpkg.com/detect-port/-/detect-port-1.0.1.tgz#3e1aa6a7ff6677bb60894b291172529d880c1e85"
+  dependencies:
+    commander "~2.8.1"
+
 detective@^4.3.1:
   version "4.3.1"
   resolved "https://registry.yarnpkg.com/detective/-/detective-4.3.1.tgz#9fb06dd1ee8f0ea4dbcc607cda39d9ce1d4f726f"