test: convert test to typescript and fixup errors this revealed

package.json

@@ -60,8 +60,8 @@
     "presize": "npm run build:js",
     "size": "terser --compress --mangle -- ./dist/index.umd.js | gzip -c | wc -c",
     "test": "npm run test:js && npm run test:types && npm run test:jsmd",
-    "pretest:js": "npm run build:js",
-    "test:js": "tape test/*.js",
+    "test:js": "ts-node -C typescript -P tsconfig.test.json -r tsconfig-paths/register node_modules/tape/bin/tape test/*.ts",
+    "pretest:jsmd": "npm run build:js",
     "test:jsmd": "jsmd readme.md",
     "pretest:types": "npm run build:types",
     "test:types": "dtslint --localTs node_modules/typescript/lib --expectOnly test/types"
@@ -72,17 +72,19 @@
     "@rollup/plugin-node-resolve": "^10.0.0",
     "@rollup/plugin-typescript": "^6.1.0",
     "@types/node": "^8.10.54",
+    "@types/tape": "^4.13.0",
     "@typescript-eslint/eslint-plugin": "^4.8.0",
     "@typescript-eslint/parser": "^4.8.0",
     "dtslint": "^4.0.5",
     "eslint": "^7.13.0",
-    "is-mergeable-object": "1.1.0",
     "is-plain-obj": "^3.0.0",
     "jsmd": "^1.0.2",
     "rimraf": "^3.0.2",
     "rollup": "^2.33.1",
     "tape": "^5.0.1",
     "terser": "^5.3.8",
+    "ts-node": "^9.0.0",
+    "tsconfig-paths": "^3.9.0",
     "tslib": "^2.0.3",
     "typescript": "^4.1.2"
   },

src/options.ts

@@ -1,7 +1,7 @@
 import isPlainObj from "is-plain-obj"
 
 import { cloneUnlessOtherwiseSpecified } from "./impl"
-import type { Property } from "./types"
+import type { FlattenAlias, Property } from "./types"
 
 /**
  * Deep merge options.
@@ -23,7 +23,7 @@ export type ExplicitOptions<O extends Options = Options> = {
 /**
  * Deep merge options with defaults applied.
  */
-export type FullOptions<O extends Options = Options> = {
+export type FullOptions<O extends Options = Options> = FlattenAlias<{
 	arrayMerge: O[`arrayMerge`] extends undefined
 		? typeof defaultArrayMerge
 		: NonNullable<O[`arrayMerge`]>
@@ -33,7 +33,7 @@ export type FullOptions<O extends Options = Options> = {
 		? typeof defaultIsMergeable
 		: NonNullable<O[`isMergeable`]>
 	cloneUnlessOtherwiseSpecified: <T>(value: T, options: FullOptions) => T
-}
+}>
 
 /**
  * A function that determins if a type is mergable.
@@ -85,5 +85,5 @@ export function getFullOptions<O extends Options>(options?: O): FullOptions<O> {
 		clone: true,
 		...overrides,
 		cloneUnlessOtherwiseSpecified,
-	} as FullOptions<O>
+	} as unknown as FullOptions<O>
 }

src/types.ts

@@ -35,7 +35,7 @@ type DeepMergeValues<T1, T2, O extends Options> = And<IsArray<T1>, IsArray<T2>>
 /**
  * Deep merge 2 non-array objects.
  */
-export type DeepMergeObjects<T1, T2, O extends Options> = FlatternAlias<
+export type DeepMergeObjects<T1, T2, O extends Options> = FlattenAlias<
 	// @see https://github.com/microsoft/TypeScript/issues/41448
 	{
 		-readonly [K in keyof T1]: DeepMergeObjectProps<ValueOfKey<T1, K>, ValueOfKey<T2, K>, O>
@@ -118,7 +118,7 @@ type MaybeLeaf<T1, T2> = Or<
  * single object.
  */
 // eslint-disable-next-line @typescript-eslint/ban-types
-type FlatternAlias<T> = {} & { [P in keyof T]: T[P] }
+export type FlattenAlias<T> = {} & { [P in keyof T]: T[P] }
 
 /**
  * Get the value of the given key in the given object.

test/custom-array-merge.js → test/custom-array-merge.ts

@@ -1,9 +1,10 @@
-const merge = require(`../`).default
-const test = require(`tape`)
+import type { Options } from "deepmerge"
+import deepmerge from "deepmerge"
+import test from "tape"
 
 test(`custom merge array`, (t) => {
 	let mergeFunctionCalled = false
-	function overwriteMerge(target, source, options) {
+	const overwriteMerge: Options[`arrayMerge`] = (target, source, options) => {
 		mergeFunctionCalled = true
 		t.equal(options.arrayMerge, overwriteMerge)
 
@@ -17,7 +18,7 @@ test(`custom merge array`, (t) => {
 		someArray: [ 1, 2, 3 ],
 	}
 
-	const actual = merge(destination, source, { arrayMerge: overwriteMerge })
+	const actual = deepmerge(destination, source, { arrayMerge: overwriteMerge })
 	const expected = {
 		someArray: [ 1, 2, 3 ],
 		someObject: { what: `yes` },
@@ -29,10 +30,8 @@ test(`custom merge array`, (t) => {
 })
 
 test(`merge top-level arrays`, (t) => {
-	function overwriteMerge(a, b) {
-		return b
-	}
-	const actual = merge([ 1, 2 ], [ 1, 2 ], { arrayMerge: overwriteMerge })
+	const overwriteMerge: Options[`arrayMerge`] = (a, b) => b
+	const actual = deepmerge([ 1, 2 ], [ 1, 2 ], { arrayMerge: overwriteMerge })
 	const expected = [ 1, 2 ]
 
 	t.deepEqual(actual, expected)
@@ -41,7 +40,7 @@ test(`merge top-level arrays`, (t) => {
 
 test(`cloner function is available for merge functions to use`, (t) => {
 	let customMergeWasCalled = false
-	function cloneMerge(target, source, options) {
+	const cloneMerge: Options[`arrayMerge`] = (target, source, options) => {
 		customMergeWasCalled = true
 		t.ok(options.cloneUnlessOtherwiseSpecified, `cloner function is available`)
 		return target.concat(source).map((element) => options.cloneUnlessOtherwiseSpecified(element, options))
@@ -60,9 +59,9 @@ test(`cloner function is available for merge functions to use`, (t) => {
 		key2: [ `four` ],
 	}
 
-	t.deepEqual(merge(target, src, { arrayMerge: cloneMerge }), expected)
+	t.deepEqual(deepmerge(target, src, { arrayMerge: cloneMerge }), expected)
 	t.ok(customMergeWasCalled)
-	t.ok(Array.isArray(merge(target, src).key1))
-	t.ok(Array.isArray(merge(target, src).key2))
+	t.ok(Array.isArray(deepmerge(target, src).key1))
+	t.ok(Array.isArray(deepmerge(target, src).key2))
 	t.end()
 })

test/custom-is-mergeable-object.js → test/custom-is-mergeable-object.ts

@@ -1,15 +1,15 @@
-const merge = require(`../`).default
-const test = require(`tape`)
+import type { Options } from "deepmerge"
+import deepmerge from "deepmerge"
+import test from "tape"
 
 test(`isMergeable function copying object over object`, (t) => {
 	const src = { key: { isMergeable: false }, baz: `yes` }
 	const target = { key: { foo: `wat` }, baz: `whatever` }
 
-	function customIsMergeable(object) {
-		return object && typeof value === `object` && object.isMergeable !== false
-	}
+	const customIsMergeable: Options[`isMergeable`] = (object) =>
+		object && typeof object === `object` && object.isMergeable !== false
 
-	const res = merge(target, src, {
+	const res = deepmerge(target, src, {
 		isMergeable: customIsMergeable,
 	})
 
@@ -22,11 +22,10 @@ test(`isMergeable function copying object over nothing`, (t) => {
 	const src = { key: { isMergeable: false, foo: `bar` }, baz: `yes` }
 	const target = { baz: `whatever` }
 
-	function customIsMergeable(object) {
-		return object && typeof value === `object` && object.isMergeable !== false
-	}
+	const customIsMergeable: Options[`isMergeable`] = (object) =>
+		object && typeof object === `object` && object.isMergeable !== false
 
-	const res = merge(target, src, {
+	const res = deepmerge(target, src, {
 		isMergeable: customIsMergeable,
 	})