Add JSDoc based types

.gitignore

@@ -1,4 +1,5 @@
 .DS_Store
+*.d.ts
 *.log
 coverage/
 node_modules/

index.js

@@ -1,14 +1,29 @@
-// Get stats for a file, list of files, or list of messages.
+/**
+ * @typedef {import('vfile').VFile} VFile
+ * @typedef {import('vfile-message').VFileMessage} VFileMessage
+ *
+ * @typedef Statistics
+ * @property {number} fatal Fatal errors (`fatal: true`)
+ * @property {number} warn warning errors (`fatal: false`)
+ * @property {number} info informational messages (`fatal: null|undefined`)
+ * @property {number} nonfatal warning + info
+ * @property {number} total nonfatal + fatal
+ */
+
+/**
+ * Get stats for a file, list of files, or list of messages.
+ *
+ * @param {Array.<VFile|VFileMessage>|VFile|VFileMessage} value
+ * @returns {Statistics}
+ */
 export function statistics(value) {
   var result = {true: 0, false: 0, null: 0}
 
   if (value) {
-    if (value[0] && value[0].messages) {
-      // Multiple vfiles.
-      countInAll(value)
+    if (Array.isArray(value)) {
+      list(value)
     } else {
-      // One vfile / messages.
-      countAll(value.messages || value)
+      one(value)
     }
   }
 
@@ -20,23 +35,29 @@ export function statistics(value) {
     total: result.true + result.false + result.null
   }
 
-  function countInAll(files) {
+  /**
+   * @param {Array.<VFile|VFileMessage>} value
+   * @returns {void}
+   */
+  function list(value) {
     var index = -1
 
-    while (++index < files.length) {
-      countAll(files[index].messages)
+    while (++index < value.length) {
+      one(value[index])
     }
   }
 
-  function countAll(messages) {
-    var index = -1
+  /**
+   * @param {VFile|VFileMessage} value
+   * @returns {void}
+   */
+  function one(value) {
+    if ('messages' in value) return list(value.messages)
 
-    while (++index < messages.length) {
-      result[
-        messages[index].fatal === undefined || messages[index].fatal === null
-          ? null
-          : Boolean(messages[index].fatal)
-      ]++
-    }
+    result[
+      value.fatal === undefined || value.fatal === null
+        ? null
+        : Boolean(value.fatal)
+    ]++
   }
 }

package.json

@@ -28,19 +28,30 @@
   "sideEffects": false,
   "type": "module",
   "main": "index.js",
+  "types": "index.d.ts",
   "files": [
+    "index.d.ts",
     "index.js"
   ],
+  "dependencies": {
+    "vfile-message": "^3.0.0"
+  },
   "devDependencies": {
-    "c8": "^7.7.2",
+    "@types/tape": "^4.0.0",
+    "c8": "^7.0.0",
     "prettier": "^2.0.0",
     "remark-cli": "^9.0.0",
     "remark-preset-wooorm": "^8.0.0",
+    "rimraf": "^3.0.0",
     "tape": "^5.0.0",
+    "type-coverage": "^2.0.0",
+    "typescript": "^4.0.0",
     "vfile": "^5.0.0",
     "xo": "^0.39.0"
   },
   "scripts": {
+    "prepack": "npm run build && npm run format",
+    "build": "rimraf \"*.d.ts\" && tsc && type-coverage",
     "format": "remark . -qfo && prettier . -w --loglevel warn && xo --fix",
     "test-api": "node test.js",
     "test-coverage": "c8 --check-coverage --branches 100 --functions 100 --lines 100 --statements 100 --reporter lcov node test.js",
@@ -65,5 +76,10 @@
     "plugins": [
       "preset-wooorm"
     ]
+  },
+  "typeCoverage": {
+    "atLeast": 100,
+    "detail": true,
+    "strict": true
   }
 }

tsconfig.json

@@ -0,0 +1,15 @@
+{
+  "include": ["*.js"],
+  "compilerOptions": {
+    "target": "ES2020",
+    "lib": ["ES2020"],
+    "module": "ES2020",
+    "moduleResolution": "node",
+    "allowJs": true,
+    "checkJs": true,
+    "declaration": true,
+    "emitDeclarationOnly": true,
+    "allowSyntheticDefaultImports": true,
+    "skipLibCheck": true
+  }
+}