Correctly skip non-plain objects

.gitignore

@@ -1,2 +1,3 @@
 node_modules
 dist
+yarn.lock

package.json

@@ -1,7 +1,7 @@
 {
 	"name": "tree-shortcut",
 	"version": "1.0.0",
-	"description": "Simplify an object tree with a shortcut. TypeScript supported. Zero dependencies.",
+	"description": "Simplify an object tree with a shortcut. TypeScript supported.",
 	"license": "MIT",
 	"repository": "papb/tree-shortcut",
 	"author": {
@@ -39,6 +39,9 @@
 		"skip",
 		"chop"
 	],
+	"dependencies": {
+		"is-plain-obj": "^2.1.0"
+	},
 	"devDependencies": {
 		"@ava/typescript": "^1.1.1",
 		"@types/lodash.clonedeep": "^4.5.6",

readme.md

@@ -1,6 +1,6 @@
-# tree-shortcut ![Build Status](https://github.com/papb/tree-shortcut/workflows/CI/badge.svg)
+# tree-shortcut ![Build Status](https://github.com/papb/tree-shortcut/workflows/CI/badge.svg) [![install size](https://packagephobia.com/badge?p=tree-shortcut)](https://packagephobia.com/result?p=tree-shortcut)
 
-> Simplify an object tree with a shortcut. TypeScript supported. Zero dependencies.
+> Simplify an object tree with a shortcut. TypeScript supported.
 
 
 ## Install

source/core.ts

@@ -1,3 +1,5 @@
+import { isPlainObject } from './is-plain-object';
+
 type AnyObject = Record<string, unknown>;
 type AnyArray = readonly any[];
 type PropOrNever<O, Prop> = Prop extends string | number ? (O extends Record<Prop, any> ? O[Prop] : never) : never;
@@ -31,13 +33,13 @@ export type TreeShortcut<
 
 function pick(tree: any, field: string): any {
 	if (Array.isArray(tree)) return tree.map(x => pick(x, field));
-	if (!tree || typeof tree !== 'object') return tree;
+	if (!isPlainObject(tree)) return tree;
 	return tree[field];
 }
 
 function treeShortcutHelper(tree: any, from: string, to: string, name: string): any {
 	if (Array.isArray(tree)) return tree.map(x => treeShortcutHelper(x, from, to, name));
-	if (!tree || typeof tree !== 'object') return tree;
+	if (!isPlainObject(tree)) return tree;
 
 	const keys = Object.keys(tree);
 	const result: any = {};

source/is-plain-object.ts

@@ -0,0 +1,5 @@
+import isPlainObject_ = require('is-plain-obj');
+
+export function isPlainObject(value: any): value is Record<string | number | symbol, unknown> {
+	return isPlainObject_(value);
+}

test/test.ts

@@ -1,6 +1,7 @@
 import test from 'ava';
 import { expectTypeOf } from 'expect-type';
 import cloneDeep = require('lodash.clonedeep');
+import { isPlainObject } from '../source/is-plain-object';
 import treeShortcut = require('../source');
 import { TreeShortcut } from '../source/core';
 
@@ -162,3 +163,23 @@ test('Does not modify input', t => {
 	t.deepEqual(tree1, tree1memo);
 	t.deepEqual(tree2, tree2memo);
 });
+
+test('Does not mess with non-plain objects', t => {
+	expectTypeOf<TreeShortcut<{ foo: { bar: Date }; qux: Date }, 'foo', 'bar', 'baz'>>()
+		.toEqualTypeOf<{ baz: Date; qux: Date }>();
+
+	const date = new Date();
+
+	// `is-plain-object` sanity check
+	t.true(isPlainObject({}));
+	t.false(isPlainObject(null));
+	t.false(isPlainObject(date));
+
+	const tree = [{ a: date, b: null, c: undefined, d: 4, e: { f: date } }];
+	const expected = [{ a: date, b: null, c: undefined, d: 4, x: date }];
+
+	t.deepEqual(
+		treeShortcut(tree, 'e', 'f', 'x'),
+		expected,
+	);
+});