Add isClientSide helper for server-side rendering

packages/client/src/renderer/index.ts

@@ -2,3 +2,4 @@ export * from './ClientRenderer'
 export * from './IClientConfig'
 export * from './IRenderer'
 export * from './IStoreFactory'
+export * from './isClientSide'

packages/client/src/renderer/isClientSide.test.ts

@@ -0,0 +1,27 @@
+import {isClientSide} from './isClientSide'
+
+describe('isClientSide', () => {
+
+  describe('client', () => {
+    it('returns true when running in browser', () => {
+      expect(isClientSide()).toBe(true)
+    })
+  })
+
+  describe('server', () => {
+
+    const g: any = global
+    const window = g.window
+    beforeEach(() => {
+      delete g.window
+    })
+
+    afterEach(() => {
+      g.window = window
+    })
+    it('returns false when running on server', () => {
+      expect(isClientSide()).toBe(false)
+    })
+  })
+
+})

packages/client/src/renderer/isClientSide.ts

@@ -0,0 +1,5 @@
+export function isClientSide() {
+  return typeof window !== 'undefined' &&
+    typeof window.document !== 'undefined' &&
+    typeof window.document.createElement === 'function'
+}