Add JSDoc based types

.gitignore

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

index.js

@@ -1,17 +1,56 @@
+/**
+ * @typedef {import('unist').Node} Node
+ * @typedef {import('unist').Parent} Parent
+ * @typedef {import('mdast').Heading} Heading
+ *
+ * @typedef {(value: string, node: Heading) => boolean} TestFunction
+ * @typedef {string|RegExp|TestFunction} Test
+ *
+ * @typedef Options
+ * @property {Test} test
+ * @property {boolean} [ignoreFinalDefinitions=false]
+ *
+ * @typedef ZoneInfo
+ * @property {number} start
+ * @property {number} end
+ * @property {Parent|null} parent
+ *
+ * @callback Handler
+ * @param {Heading|undefined} start
+ * @param {Array.<Node>} between
+ * @param {Node|undefined} end
+ * @param {ZoneInfo} info
+ */
+
 import {toString} from 'mdast-util-to-string'
 
-// Search `node` with `options` and invoke `callback`.
+/**
+ * Search `node` with `options` and invoke `callback`.
+ *
+ * @param {Node} node
+ * @param {Test|Options} options
+ * @param {Handler} handler
+ */
 // eslint-disable-next-line complexity
-export function headingRange(node, options, callback) {
+export function headingRange(node, options, handler) {
   var test = options
-  var children = node.children
+  /** @type {Array.<Node>} */
+  // @ts-ignore looks like children.
+  var children = node.children || []
   var index = -1
+  /** @type {boolean} */
   var ignoreFinalDefinitions
+  /** @type {number} */
   var depth
+  /** @type {number} */
   var start
+  /** @type {number} */
   var end
+  /** @type {Array.<Node>} */
   var nodes
+  /** @type {Array.<Node>} */
   var result
+  /** @type {Node} */
   var child
 
   // Object, not regex.
@@ -48,7 +87,9 @@ export function headingRange(node, options, callback) {
         break
       }
 
+      // @ts-ignore looks like a heading.
       if (!depth && test(toString(child), child)) {
+        // @ts-ignore looks like a heading.
         depth = child.depth
         start = index
         // Assume no end heading is found.
@@ -68,7 +109,8 @@ export function headingRange(node, options, callback) {
       }
     }
 
-    nodes = callback(
+    nodes = handler(
+      // @ts-ignore `start` points to a heading.
       children[start],
       children.slice(start + 1, end),
       children[end],
@@ -94,11 +136,19 @@ export function headingRange(node, options, callback) {
   }
 }
 
-// Wrap an expression into an assertion function.
+/**
+ * Wrap an expression into an assertion function.
+ * @param {RegExp} expression
+ * @returns {(value: string) => boolean}
+ */
 function wrapExpression(expression) {
   return assertion
 
-  // Assert `value` matches the bound `expression`.
+  /**
+   * Assert `value` matches the bound `expression`.
+   * @param {string} value
+   * @returns {boolean}
+   */
   function assertion(value) {
     return expression.test(value)
   }

package.json

@@ -27,26 +27,36 @@
   "sideEffects": false,
   "type": "module",
   "main": "index.js",
+  "types": "index.d.ts",
   "files": [
+    "index.d.ts",
     "index.js"
   ],
   "dependencies": {
+    "@types/mdast": "^3.0.0",
+    "@types/unist": "^2.0.0",
     "mdast-util-to-string": "^3.0.0"
   },
   "devDependencies": {
+    "@types/tape": "^4.0.0",
     "c8": "^7.0.0",
     "prettier": "^2.0.0",
     "remark": "^13.0.0",
     "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": "^0.39.0"
   },
   "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",
-    "test": "npm run format && npm run test-coverage"
+    "test": "npm run build && npm run format && npm run test-coverage"
   },
   "prettier": {
     "tabWidth": 2,
@@ -67,5 +77,10 @@
     "plugins": [
       "preset-wooorm"
     ]
+  },
+  "typeCoverage": {
+    "atLeast": 100,
+    "detail": true,
+    "strict": true
   }
 }

test.js

@@ -1,3 +1,9 @@
+/**
+ * @typedef {import('tape').Test} Test
+ * @typedef {import('unist').Node} Node
+ * @typedef {import('./index.js').Test | import('./index.js').Options} Options
+ */
+
 import test from 'tape'
 import remark from 'remark'
 import {headingRange} from './index.js'
@@ -47,6 +53,7 @@ test('mdast-util-heading-range()', function (t) {
     process(
       t,
       ['# Fo', '', '## Fooooo', '', 'Bar', '', '# Fo', ''].join('\n'),
+      /** @type {Options} */
       function (value) {
         return value.toLowerCase().indexOf('foo') === 0
       }
@@ -161,7 +168,7 @@ test('mdast-util-heading-range()', function (t) {
   remark()
     .use(function () {
       return function (node) {
-        headingRange(node, 'foo', function (start, nodes, end) {
+        headingRange(node, 'foo', function (start, _, end) {
           return [start, {type: 'thematicBreak'}, end]
         })
       }
@@ -184,8 +191,7 @@ test('mdast-util-heading-range()', function (t) {
       return function (node) {
         headingRange(node, 'foo', function (start, nodes, end) {
           t.equal(nodes.length, 3)
-
-          return [start].concat(nodes, end)
+          return [start, ...nodes, end]
         })
       }
     })
@@ -303,15 +309,20 @@ test('mdast-util-heading-range()', function (t) {
   )
 })
 
+/**
+ * @param {Test} t
+ * @param {string} value
+ * @param {Options} options
+ */
 function process(t, value, options) {
   return remark()
     .use(function () {
       return function (node) {
-        headingRange(node, options, function (start, nodes, end, scope) {
+        headingRange(node, options, function (start, _, end, scope) {
           t.equal(typeof scope.start, 'number')
           t.assert(typeof scope.end === 'number' || scope.end === null)
           t.equal(scope.parent.type, 'root')
-          return [start].concat([end])
+          return [start, 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
+  }
+}