Validate the input object

Closes #15

index.js

@@ -1,14 +1,15 @@
 'use strict';
 
+const isObject = value => typeof value === 'object' && value !== null;
+
 // Customized for this use-case
-const isObject = value =>
-	typeof value === 'object' &&
-	value !== null &&
+const isObjectCustom = value =>
+	isObject(value) &&
 	!(value instanceof RegExp) &&
 	!(value instanceof Error) &&
 	!(value instanceof Date);
 
-const mapObject = (object, fn, options, isSeen = new WeakMap()) => {
+const mapObject = (object, mapper, options, isSeen = new WeakMap()) => {
 	options = {
 		deep: false,
 		target: {},
@@ -24,18 +25,18 @@ const mapObject = (object, fn, options, isSeen = new WeakMap()) => {
 	const {target} = options;
 	delete options.target;
 
-	const mapArray = array => array.map(element => isObject(element) ? mapObject(element, fn, options, isSeen) : element);
+	const mapArray = array => array.map(element => isObjectCustom(element) ? mapObject(element, mapper, options, isSeen) : element);
 	if (Array.isArray(object)) {
 		return mapArray(object);
 	}
 
 	for (const [key, value] of Object.entries(object)) {
-		let [newKey, newValue] = fn(key, value, object);
+		let [newKey, newValue] = mapper(key, value, object);
 
-		if (options.deep && isObject(newValue)) {
+		if (options.deep && isObjectCustom(newValue)) {
 			newValue = Array.isArray(newValue) ?
 				mapArray(newValue) :
-				mapObject(newValue, fn, options, isSeen);
+				mapObject(newValue, mapper, options, isSeen);
 		}
 
 		target[newKey] = newValue;
@@ -44,4 +45,10 @@ const mapObject = (object, fn, options, isSeen = new WeakMap()) => {
 	return target;
 };
 
-module.exports = mapObject;
+module.exports = (object, mapper, options) => {
+	if (!isObject(object)) {
+		throw new TypeError(`Expected an object, got \`${object}\` (${typeof object})`);
+	}
+
+	return mapObject(object, mapper, options);
+};

test.js

@@ -42,8 +42,8 @@ test('deep option', t => {
 		]
 	};
 
-	const fn = (key, value) => [key, typeof value === 'number' ? value * 2 : value];
-	const actual = mapObject(object, fn, {deep: true});
+	const mapper = (key, value) => [key, typeof value === 'number' ? value * 2 : value];
+	const actual = mapObject(object, mapper, {deep: true});
 	t.deepEqual(actual, expected);
 });
 
@@ -74,8 +74,8 @@ test('nested arrays', t => {
 		]
 	};
 
-	const fn = (key, value) => [key, typeof value === 'number' ? value * 2 : value];
-	const actual = mapObject(object, fn, {deep: true});
+	const mapper = (key, value) => [key, typeof value === 'number' ? value * 2 : value];
+	const actual = mapObject(object, mapper, {deep: true});
 	t.deepEqual(actual, expected);
 });
 
@@ -90,8 +90,8 @@ test('handles circular references', t => {
 	object.array2 = object.array;
 	object.array.push(object);
 
-	const fn = (key, value) => [key.toUpperCase(), value];
-	const actual = mapObject(object, fn, {deep: true});
+	const mapper = (key, value) => [key.toUpperCase(), value];
+	const actual = mapObject(object, mapper, {deep: true});
 
 	const expected = {
 		ONE: 1,
@@ -105,3 +105,9 @@ test('handles circular references', t => {
 
 	t.deepEqual(actual, expected);
 });
+
+test('validates input', t => {
+	t.throws(() => {
+		mapObject(1, () => {});
+	}, TypeError);
+});