Add JSDoc based types

.gitignore

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

index.js

@@ -1,17 +1,38 @@
+/**
+ * @typedef {import('unist').Parent} Parent
+ * @typedef {import('unist').Node} Node
+ *
+ * @typedef {Node} Proxy
+ * @property {parent|null} parent
+ */
+
+/** @type {WeakMap<Node, Proxy>} */
 var cache = new WeakMap()
 
-export function parents(ast) {
-  return wrapNode(ast, null)
+/**
+ * @param {Node} tree
+ * @returns {Proxy}
+ */
+export function parents(tree) {
+  return wrapNode(tree, null)
 }
 
+/**
+ * @param {Node} node
+ * @param {Parent|null} parent
+ * @returns {Proxy}
+ */
 function wrapNode(node, parent) {
+  /** @type {Node} */
   var proxy
+  /** @type {string} */
   var key
 
   if (cache.has(node)) {
     return cache.get(node)
   }
 
+  // @ts-ignore Assume `node` is a valid node.
   proxy = {}
 
   for (key in node) {
@@ -48,13 +69,15 @@ function wrapNode(node, parent) {
     return parent
   }
 
+  /**
+   * @param {Parent} newParent
+   */
   function setParent(newParent) {
     parent = newParent
   }
 
   function getChildren() {
-    return node.children.map(function (child) {
-      return wrapNode(child, proxy)
-    })
+    // @ts-ignore `node` is a parent.
+    return node.children.map((/** @type {Node} */ c) => wrapNode(c, proxy))
   }
 }

package.json

@@ -30,23 +30,34 @@
   "sideEffects": false,
   "type": "module",
   "main": "index.js",
+  "types": "index.d.ts",
   "files": [
+    "index.d.ts",
     "index.js"
   ],
+  "dependencies": {
+    "@types/unist": "^2.0.0"
+  },
   "devDependencies": {
+    "@types/tape": "^4.0.0",
     "c8": "^7.0.0",
     "clone": "^2.0.0",
     "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",
     "xo": "^0.38.0"
   },
   "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",
-    "test": "npm run format && npm run test-coverage"
+    "test": "npm run build && npm run format && npm run test-coverage"
   },
   "prettier": {
     "tabWidth": 2,
@@ -59,6 +70,7 @@
   "xo": {
     "prettier": true,
     "rules": {
+      "capitalized-comments": "off",
       "no-var": "off",
       "prefer-arrow-callback": "off"
     }
@@ -67,5 +79,10 @@
     "plugins": [
       "preset-wooorm"
     ]
+  },
+  "typeCoverage": {
+    "atLeast": 100,
+    "detail": true,
+    "strict": true
   }
 }

test.js

@@ -24,7 +24,12 @@ test('immutable', function (t) {
   t.deepEqual(ast, original, 'original AST is unchanged')
   t.notEqual(root, ast, 'returns a different object')
   t.deepEqual(root, ast, 'structurally equivalent')
-  t.false(ast.children[0].parent, 'original AST does not obtain parent links')
+  t.equal(
+    // type-coverage:ignore-next-line, yeah, that’s expected.
+    ast.children[0].parent,
+    undefined,
+    'original AST does not obtain parent links'
+  )
   t.end()
 })
 

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
+  }
+}