X-Git-Url: https://git.ladys.computer/Pisces/blobdiff_plain/0fb1e53a1e78a6bf490cd95cf92a744d3ac6171f..beab7268e7673b036222e64aac924f850e2b976e:/object.js

diff --git a/object.js b/object.js
index 9c0c973..ee3d51d 100644
--- a/object.js
+++ b/object.js
@@ -14,6 +14,7 @@ import {
   toFunctionName,
 } from "./function.js";
 import {
+  IS_CONCAT_SPREADABLE,
   ITERATOR,
   SPECIES,
   toLength,
@@ -810,6 +811,32 @@ export const isArraylikeObject = ($) => {
   }
 };
 
+export const {
+  /**
+   * Returns whether the provided value is spreadable during array
+   * concatenation.
+   *
+   * This is also used to determine which things should be treated as
+   * collections.
+   */
+  isConcatSpreadableObject,
+} = (() => {
+  const { isArray } = Array;
+
+  return {
+    isConcatSpreadableObject: ($) => {
+      if (type($) !== "object") {
+        // The provided value is not an object.
+        return false;
+      } else {
+        // The provided value is an object.
+        const spreadable = $[IS_CONCAT_SPREADABLE];
+        return spreadable !== undefined ? !!spreadable : isArray($);
+      }
+    },
+  };
+})();
+
 /**
  * Returns whether the provided object is extensible.
  *