Add TypeScript definitions and test

index.d.ts

@@ -0,0 +1,14 @@
+declare function deepmerge<T>(x: Partial<T>, y: Partial<T>, options?: deepmerge.Options): T;
+declare function deepmerge<T1, T2>(x: Partial<T1>, y: Partial<T2>, options?: deepmerge.Options): T1 & T2;
+
+declare namespace deepmerge {
+	export interface Options {
+		arrayMerge?(target: any[], source: any[], options?: Options): any[];
+		clone?: boolean;
+		isMergeableObject?(value: object): boolean;
+	}
+
+	export function all (objects: object[], options?: Options): object;
+}
+
+export default deepmerge;

package.json

@@ -23,7 +23,7 @@
   },
   "scripts": {
     "build": "rollup -c",
-    "test": "npm run build && tap test/*.js && jsmd readme.md",
+    "test": "npm run build && tap test/*.js && jsmd readme.md && tsc --noEmit test/typescript.ts",
     "size": "npm run build && uglifyjs --compress --mangle -- ./dist/umd.js | gzip -c | wc -c"
   },
   "devDependencies": {
@@ -34,6 +34,7 @@
     "rollup-plugin-commonjs": "8.2.1",
     "rollup-plugin-node-resolve": "3.0.0",
     "tap": "~7.1.2",
+    "typescript": "=2.2.2",
     "uglify-js": "^3.3.12"
   },
   "license": "MIT"

test/typescript.ts

@@ -0,0 +1,50 @@
+import merge from '../';
+
+const x = {
+	foo: 'abc',
+	bar: 'def',
+}
+
+const y = {
+	foo: 'cba',
+	bar: 'fed',
+}
+
+const z = {
+	baz: '123',
+	quux: '456',
+}
+
+let merged1 = merge(x, y);
+let merged2 = merge(x, z);
+let merged3 = merge.all([ x, y, z ]);
+
+merged1.foo;
+merged1.bar;
+merged2.foo;
+merged2.baz;
+
+const options1: merge.Options = {
+	clone: true,
+	isMergeableObject (obj) {
+		return true;
+	},
+};
+
+const options2: merge.Options = {
+	arrayMerge (target, source, options) {
+		target.length;
+		source.length;
+		options.isMergeableObject(target);
+
+		return [];
+	},
+	clone: true,
+	isMergeableObject (obj) {
+		return true;
+	},
+};
+
+merged1 = merge(x, y, options1);
+merged2 = merge(x, z, options2);
+merged3 = merge([x, y, z], options1);