feature: support isFragment

compat/src/index.d.ts

@@ -107,6 +107,7 @@ declare namespace React {
 		...children: preact.ComponentChildren[]
 	) => preact.VNode<any>;
 	export function isValidElement(element: any): boolean;
+	export function isFragment(element: any): boolean;
 	export function findDOMNode(
 		component: preact.Component | Element
 	): Element | null;

compat/src/index.js

@@ -54,6 +54,15 @@ function isValidElement(element) {
 	return !!element && element.$$typeof === REACT_ELEMENT_TYPE;
 }
 
+/**
+ * Check if the passed element is a Fragment node.
+ * @param {*} element The element to check
+ * @returns {boolean}
+ */
+function isFragment(element) {
+	return isValidElement(element) && element.type === Fragment;
+}
+
 /**
  * Wrap `cloneElement` to abort if the passed element is not a valid element and apply
  * all vnode normalizations.
@@ -185,6 +194,7 @@ export {
 	createRef,
 	Fragment,
 	isValidElement,
+	isFragment,
 	findDOMNode,
 	Component,
 	PureComponent,
@@ -231,6 +241,7 @@ export default {
 	createRef,
 	Fragment,
 	isValidElement,
+	isFragment,
 	findDOMNode,
 	Component,
 	PureComponent,

compat/test/browser/isFragment.test.js

@@ -0,0 +1,22 @@
+import { createElement as preactCreateElement, Fragment } from 'preact';
+import React, { isFragment } from 'preact/compat';
+
+describe('isFragment', () => {
+	it('should check return false for invalid arguments', () => {
+		expect(isFragment(null)).to.equal(false);
+		expect(isFragment(false)).to.equal(false);
+		expect(isFragment(true)).to.equal(false);
+		expect(isFragment('foo')).to.equal(false);
+		expect(isFragment(123)).to.equal(false);
+		expect(isFragment([])).to.equal(false);
+		expect(isFragment({})).to.equal(false);
+	});
+
+	it('should detect a preact vnode', () => {
+		expect(isFragment(preactCreateElement(Fragment, {}))).to.equal(true);
+	});
+
+	it('should detect a compat vnode', () => {
+		expect(isFragment(React.createElement(Fragment, {}))).to.equal(true);
+	});
+});