Verify that the entry module argument for quick commands exists, to a…

…void a confusing error message

Fixes #441

CHANGES.md

@@ -1,3 +1,9 @@
+# Unreleased (in `master`)
+
+## Changed
+
+- Validate that the entry module for quick commands (`nwb react`, `nwb preact`, `nwb inferno`) exists, to avoid a confusing error message [[#441](https://github.com/insin/nwb/issues/441)]
+
 # 0.24.3 / 2020-03-14
 
 ## Changed

src/quickCommands.js

@@ -1,4 +1,5 @@
 // @flow
+import fs from 'fs'
 import path from 'path'
 
 import runSeries from 'run-series'
@@ -40,6 +41,9 @@ export function build(args: Object, appConfig: QuickAppConfig, cb: ErrBack) {
   if (args._.length === 1) {
     return cb(new UserError('An entry module must be specified.'))
   }
+  if (!fs.existsSync(args._[1])) {
+    return cb(new UserError(`${args._[1]} does not exist.`))
+  }
 
   let dist = args._[2] || 'dist'
 
@@ -187,6 +191,9 @@ export function serve(args: Object, appConfig: QuickAppConfig, cb: ErrBack) {
   if (args._.length === 1) {
     return cb(new UserError('An entry module must be specified.'))
   }
+  if (!fs.existsSync(args._[1])) {
+    return cb(new UserError(`${args._[1]} does not exist.`))
+  }
 
   runSeries([
     (cb) => install(appConfig.getQuickDependencies(), {args, check: true}, cb),