add deep equality utility

src/utils.js

@@ -37,6 +37,21 @@ export function concat(aaa, bbb) {
   }
 }
 
+/**
+ * Deep equality comparison
+ * 
+ * @param {any} a 
+ * @param {any} b 
+ * @returns {boolean}
+ */
+export function equals(a, b) {
+  if (a === b) return true;
+  if (!a || !b || typeof a !== typeof b) return false;
+  return Array.isArray(a) 
+    ? a.length === b.length && a.every((v, i) => equals(v, b[i]))
+    : Object.keys(a).length === Object.keys(b).length && Object.keys(a).every(k => equals(a[k], b[k]));
+}
+
 /**
  * Get the byte length of a URL using a HEAD request.
  * If requestInit is provided, it will be passed to fetch.