feat: added isMemo to compact to allow compatibility with react-is dependant libraries

compat/src/index.d.ts

@@ -115,14 +115,16 @@ declare namespace React {
 	) => preact.VNode<any>;
 	export function isValidElement(element: any): boolean;
 	export function isFragment(element: any): boolean;
+	export function isMemo(element: any): boolean;
 	export function findDOMNode(
 		component: preact.Component | Element
 	): Element | null;
 
-	export abstract class PureComponent<P = {}, S = {}, SS = any> extends preact.Component<
-		P,
-		S
-	> {
+	export abstract class PureComponent<
+		P = {},
+		S = {},
+		SS = any
+	> extends preact.Component<P, S> {
 		isPureReactComponent: boolean;
 	}
 
@@ -174,9 +176,9 @@ declare namespace React {
 
 	export type ComponentPropsWithRef<
 		C extends ComponentType<any> | keyof JSXInternal.IntrinsicElements
-	> = C extends (new(props: infer P) => Component<any, any>)
-	? PropsWithoutRef<P> & RefAttributes<InstanceType<C>>
-	: ComponentProps<C>;
+	> = C extends new (props: infer P) => Component<any, any>
+		? PropsWithoutRef<P> & RefAttributes<InstanceType<C>>
+		: ComponentProps<C>;
 
 	export function flushSync<R>(fn: () => R): R;
 	export function flushSync<A, R>(fn: (a: A) => R, a: A): R;

compat/src/index.js

@@ -63,6 +63,21 @@ function isFragment(element) {
 	return isValidElement(element) && element.type === Fragment;
 }
 
+/**
+ * Check if the passed element is a Memo node.
+ * @param {*} element The element to check
+ * @returns {boolean}
+ */
+function isMemo(element) {
+	return (
+		!!element &&
+		!!element.displayName &&
+		(typeof element.displayName === 'string' ||
+			element.displayName instanceof String) &&
+		element.displayName.startsWith('Memo(')
+	);
+}
+
 /**
  * Wrap `cloneElement` to abort if the passed element is not a valid element and apply
  * all vnode normalizations.
@@ -215,6 +230,7 @@ export {
 	Fragment,
 	isValidElement,
 	isFragment,
+	isMemo,
 	findDOMNode,
 	Component,
 	PureComponent,
@@ -263,6 +279,7 @@ export default {
 	isValidElement,
 	isElement,
 	isFragment,
+	isMemo,
 	findDOMNode,
 	Component,
 	PureComponent,

compat/test/browser/isMemo.test.js

@@ -0,0 +1,37 @@
+import { createElement as preactCreateElement, Fragment } from 'preact';
+import React, { createElement, isMemo, memo } from 'preact/compat';
+
+describe('isMemo', () => {
+	it('should check return false for invalid arguments', () => {
+		expect(isMemo(null)).to.equal(false);
+		expect(isMemo(false)).to.equal(false);
+		expect(isMemo(true)).to.equal(false);
+		expect(isMemo('foo')).to.equal(false);
+		expect(isMemo(123)).to.equal(false);
+		expect(isMemo([])).to.equal(false);
+		expect(isMemo({})).to.equal(false);
+	});
+
+	it('should detect a preact memo', () => {
+		function Foo() {
+			return <h1>Hello World</h1>;
+		}
+		let App = memo(Foo);
+		expect(isMemo(App)).to.equal(true);
+	});
+
+	it('should not detect a normal element', () => {
+		function Foo() {
+			return <h1>Hello World</h1>;
+		}
+		expect(isMemo(Foo)).to.equal(false);
+	});
+
+	it('should detect a preact vnode as false', () => {
+		expect(isMemo(preactCreateElement(Fragment, {}))).to.equal(false);
+	});
+
+	it('should detect a compat vnode as false', () => {
+		expect(isMemo(React.createElement(Fragment, {}))).to.equal(false);
+	});
+});