fix: FallbackComponent type (#62)

* test: add failing tests

* chore: add react-is as dep

* fix: support all kind of component

Closes #61
To fix the issue I have used the library from facebook 'react-is'.
With this library we can check if the FallbackComponent is a real component.
A component is not alwasy a function, but can be also object

* chore: remove react-is dep

* fix: check FallbackComponent if is defined instead of using react-is

* test: simplify test after review

Author: marcosvega91

src/__tests__/index.js

@@ -348,3 +348,39 @@ test('supports automatic reset of error boundary when resetKeys change', () => {
   expect(screen.queryByRole('alert')).not.toBeInTheDocument()
   expect(console.error).not.toHaveBeenCalled()
 })
+
+test('should support not only function as FallbackComponent', () => {
+  const FancyFallback = React.forwardRef(({error}) => (
+    <div>
+      <p>Everything is broken. Try again</p>
+      <pre>{error.message}</pre>
+    </div>
+  ))
+  FancyFallback.displayName = 'FancyFallback'
+
+  expect(() =>
+    render(
+      <ErrorBoundary FallbackComponent={FancyFallback}>
+        <Bomb />
+      </ErrorBoundary>,
+    ),
+  ).not.toThrow()
+
+  expect(
+    screen.getByText('Everything is broken. Try again'),
+  ).toBeInTheDocument()
+
+  console.error.mockClear()
+})
+
+test('should throw error if FallbackComponent is not valid', () => {
+  expect(() =>
+    render(
+      <ErrorBoundary FallbackComponent={{}}>
+        <Bomb />
+      </ErrorBoundary>,
+    ),
+  ).toThrowError(/Element type is invalid/i)
+
+  console.error.mockClear()
+})

src/index.js

@@ -39,7 +39,7 @@ class ErrorBoundary extends React.Component {
         return fallback
       } else if (typeof fallbackRender === 'function') {
         return fallbackRender(props)
-      } else if (typeof FallbackComponent === 'function') {
+      } else if (FallbackComponent) {
         return <FallbackComponent {...props} />
       } else {
         throw new Error(