Add Global.hermesInternal (facebook#613)

* Add Global.hermesInternal Closes facebook#610 * Update Global.md
jfrolich · Sep 23, 2019 · 6c6772b · 6c6772b
1 parent 6abb155
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diff --git a/src/apis/Global.md b/src/apis/Global.md
@@ -20,3 +20,14 @@ else {
   "This is production"
 }
 ```
+
+## `Global.hermesInternal`
+
+This is the `HermesInternal` value known in JavaScript as
+[`global.HermesInternal`](https://facebook.github.io/react-native/docs/hermes).
+
+You can use it like this:
+
+```reason
+let isHermes = () => Global.hermesInternal != None;
+```
diff --git a/src/apis/Global.re b/src/apis/Global.re
@@ -1 +1,4 @@
 [@bs.val] external __DEV__: bool = "__DEV__";
+
+[@bs.scope "global"] [@bs.val]
+external hermesInternal: option(Js.t('a)) = "hermesInternal";