Add JSDoc based types

.gitignore

@@ -1,5 +1,6 @@
 coverage/
 node_modules/
 .DS_Store
+*.d.ts
 *.log
 yarn.lock

index.js

@@ -1 +1,5 @@
+/**
+ * @typedef {import('./lib/index.js').Options} Options
+ */
+
 export {args} from './lib/index.js'

lib/index.js

@@ -1,14 +1,18 @@
+/**
+ * @typedef {import('unified-engine').Options} EngineOptions
+ * @typedef {import('unified-engine/lib/index.js').Context} EngineContext
+ * @typedef {import('unified-engine').Callback} EngineCallback
+ * @typedef {import('./options.js').Options} Options
+ */
+
 import stream from 'stream'
 import chalk from 'chalk'
 import chokidar from 'chokidar'
 import {engine} from 'unified-engine'
 import {options} from './options.js'
 
-const noop = Function.prototype
-
 // Fake TTY stream.
-const ttyStream = new stream.Readable()
-ttyStream.isTTY = true
+const ttyStream = Object.assign(new stream.Readable(), {isTTY: true})
 
 // Exit, lazily, with the correct exit status code.
 let exitStatus = 0
@@ -18,13 +22,21 @@ process.on('exit', onexit)
 // Handle uncaught errors, such as from unexpected async behaviour.
 process.on('uncaughtException', fail)
 
-// Start the CLI.
+/**
+ * Start the CLI.
+ *
+ * @param {Options} cliConfig
+ */
 export function args(cliConfig) {
+  /** @type {EngineOptions & {help: boolean, helpMessage: string, watch: boolean, version: boolean}} */
   let config
-  let output
+  /** @type {chokidar.FSWatcher|undefined} */
   let watcher
+  /** @type {boolean|string|undefined} */
+  let output
 
   try {
+    // @ts-expect-error: Close enough.
     config = options(process.argv.slice(2), cliConfig)
   } catch (error) {
     return fail(error, true)
@@ -83,15 +95,19 @@ export function args(cliConfig) {
   // Initial run.
   engine(config, done)
 
-  // Handle complete run.
+  /**
+   * Handle complete run.
+   *
+   * @type {EngineCallback}
+   */
   function done(error, code, context) {
     if (error) {
       clean()
       fail(error)
     } else {
-      exitStatus = code
+      exitStatus = code || 0
 
-      if (config.watch && !watcher) {
+      if (config.watch && !watcher && context) {
         subscribe(context)
       }
     }
@@ -101,25 +117,30 @@ export function args(cliConfig) {
   function clean() {
     if (watcher) {
       watcher.close()
-      watcher = null
+      watcher = undefined
     }
   }
 
-  // Subscribe a chokidar watcher to all processed files.
+  /**
+   * Subscribe a chokidar watcher to all processed files.
+   *
+   * @param {EngineContext} context
+   */
   function subscribe(context) {
     watcher = chokidar
+      // @ts-expect-error: `fileSet` is available.
       .watch(context.fileSet.origins, {cwd: config.cwd, ignoreInitial: true})
       .on('error', done)
-      .on('change', onchange)
+      .on('change', (filePath) => {
+        config.files = [filePath]
+        engine(config, done)
+      })
 
     process.on('SIGINT', onsigint)
 
-    function onchange(filePath) {
-      config.files = [filePath]
-
-      engine(config, done)
-    }
-
+    /**
+     * Handle a SIGINT.
+     */
     function onsigint() {
       // Hide the `^C` in terminal.
       process.stderr.write('\n', noop)
@@ -136,11 +157,16 @@ export function args(cliConfig) {
   }
 }
 
-// Print an error, optionally with stack.
+/**
+ * Print an error, optionally with stack.
+ *
+ * @param {Error} error
+ * @param {boolean} [pretty=false]
+ */
 function fail(error, pretty) {
   // Old versions of Node
   /* c8 ignore next 1 */
-  const message = (pretty ? String(error).trim() : error.stack) || error
+  const message = String((pretty ? error : error.stack) || error)
 
   exitStatus = 1
 
@@ -152,3 +178,5 @@ function onexit() {
   process.exit(exitStatus)
   /* eslint-enable unicorn/no-process-exit */
 }
+
+function noop() {}