Fix double encoding in nested query parameters at 3+ levels

src/url.ts

@@ -31,13 +31,13 @@ function stringify(
         return queryString;
       }
 
-      const encodedKey = prefix
-        ? encodeURIComponent(`${prefix}[${key}]`)
-        : encodeURIComponent(key);
+      // Build the unencoded key path first
+      const keyPath = prefix ? `${prefix}[${key}]` : key;
 
       // Check if value is an object and we haven't exceeded max depth
       if (typeof value === "object" && value !== null && depth < maxDepth) {
-        const nestedQuery = stringifyRecursive(value, encodedKey, depth + 1);
+        // Pass unencoded keyPath as prefix to prevent double encoding in recursive calls
+        const nestedQuery = stringifyRecursive(value, keyPath, depth + 1);
 
         // Only append if nestedQuery has content
         if (!nestedQuery) {
@@ -48,6 +48,8 @@ function stringify(
           ? `${queryString}${separator}${nestedQuery}`
           : nestedQuery;
       } else {
+        // Encode only once at the leaf level
+        const encodedKey = encodeURIComponent(keyPath);
         const encodedValue =
           typeof value === "object" && value !== null
             ? ""

tests/url.spec.ts

@@ -195,4 +195,27 @@ describe("DynamicURL", () => {
     expect(result).toBe("https://example.com?citizen=robespierre");
     expect(result).not.toContain("emptyNested");
   });
+
+  test("should not double-encode nested objects at 3+ levels deep", () => {
+    const url = new DynamicURL("https://example.com");
+    url.setQueryParams({
+      level1: {
+        level2: {
+          level3: "value",
+        },
+      },
+    });
+
+    const result = url.resolve();
+    // Should have single encoding: level1[level2][level3]
+    expect(result).toBe(
+      "https://example.com?level1%5Blevel2%5D%5Blevel3%5D=value"
+    );
+
+    // Verify decoded key is correct
+    const queryString = result.split("?")[1];
+    const params = new URLSearchParams(queryString);
+    const keys = Array.from(params.keys());
+    expect(keys[0]).toBe("level1[level2][level3]");
+  });
 });