diff --git a/javascript/spread-the-rest-with-es6.md b/javascript/spread-the-rest-with-es6.md
index 847c07a..9b1caf5 100644
--- a/javascript/spread-the-rest-with-es6.md
+++ b/javascript/spread-the-rest-with-es6.md
@@ -26,4 +26,8 @@ signature to grab specific items from an incoming object argument without
 losing track of the rest -- this is especially useful in React.js
 development when dealing with incoming props.
 
+This is a [stage 3
+feature](https://github.com/tc39/proposal-object-rest-spread) and may not be
+available in your particular environment.
+
 See a [live example here](https://codesandbox.io/s/ov2xr1o12y).