Add Check The Type Of A Child Component as a React til

react/check-the-type-of-a-child-component.md

@@ -0,0 +1,33 @@
+# Check The Type Of A Child Component
+
+There is a simple way to check the type of a child component.
+
+```javascript
+import React from 'react';
+
+const Hello = () => <h1>Hello</h1>;
+
+const Greeting = ({ children }) => {
+  let hello;
+  React.Children.forEach(children, child => {
+    if(child.type === Hello) {
+      hello = child;
+    }
+  });
+
+  return hello;
+};
+```
+
+This is a comparison of the child's type to the component constant we are
+looking for.
+
+This comparison is not the most robust. For instance, Gatsby does something
+internally that throws off this comparison. Here is a more robust
+comparison.
+
+```javascript
+if(child.type === Hello || child.type === <Hello />.type)
+```
+
+[source](https://github.com/gatsbyjs/gatsby/issues/3486)