fix NodeJS Client is using undefined http agent issue (#4453)

* test: add unit test to reproduce the issue

* fix: change the update line order

* chore: code lint fix

* Update .changes/next-release/bugfix-NodeJS-Client-80bdf3e3.json

Co-authored-by: Trivikram Kamat <[email protected]>

---------

Co-authored-by: Ray Wang <>
Co-authored-by: Trivikram Kamat <[email protected]>

Author: pivstone

.changes/next-release/bugfix-NodeJS-Client-80bdf3e3.json

@@ -0,0 +1,5 @@
+{
+  "type": "bugfix",
+  "category": "node",
+  "description": "use undefined node http agent if explicitly passed by user"
+}

lib/http/node.js

@@ -32,13 +32,14 @@ AWS.NodeHttpClient = AWS.util.inherit({
       path: pathPrefix + httpRequest.path
     };
 
+    AWS.util.update(options, httpOptions);
+
     if (!httpOptions.agent) {
       options.agent = this.getAgent(useSSL, {
         keepAlive: process.env[CONNECTION_REUSE_ENV_NAME] === '1' ? true : false
       });
     }
 
-    AWS.util.update(options, httpOptions);
     delete options.proxy; // proxy isn't an HTTP option
     delete options.timeout; // timeout isn't an HTTP option