enh: use type guard to target (#50)

src/bin.ts

@@ -12,8 +12,9 @@ import { render as reactRender } from './renderers/react.js'
 import { render as astroRender } from './renderers/astro.js'
 
 type Extension = '.tsx' | '.astro'
+type Target = 'react' | 'hono' | 'astro';
 
-function createFile(mist: string, target: string, ext: Extension) {
+function createFile(mist: string, target: Target, ext: Extension) {
  try {
  const data = parse(fs.readFileSync(mist, 'utf8'))
  const name = path.basename(mist, '.mist.css')
@@ -79,15 +80,16 @@ if (!(await fsPromises.stat(dir)).isDirectory()) {
  process.exit(1)
 }
 
-if (['react', 'hono', 'astro'].includes(values.target!) === false) {
+const { target } = values;
+if (target !== 'react' && target !== 'hono' && target !== 'astro') {
  console.error('Invalid render option')
  usage()
  process.exit(1)
 }
 
 // Set extension
 let ext: Extension
-switch (values.target) {
+switch (target) {
  case 'react':
  ext = '.tsx'
  console.log('Rendering React components')
@@ -115,15 +117,15 @@ if (values.watch) {
  console.log('Watching for changes')
  chokidar
  .watch('**/*.mist.css')
- .on('change', (file) => createFile(file, values.target!, ext))
+ .on('change', (file) => createFile(file, target, ext))
  .on('unlink', (file) => {
  fsPromises.unlink(file.replace(/\.css$/, ext)).catch(() => false)
  })
 }
 
 // Build out files
 ;(await globby('**/*.mist.css')).forEach((mist) =>
- createFile(mist, values.target!, ext),
+ createFile(mist, target, ext),
 )
 
 // Clean out files without a matching mist file