Prefer native URL instead of legacy url.resolve.

index.js

@@ -6,6 +6,8 @@ var Writable = require("stream").Writable;
 var assert = require("assert");
 var debug = require("./debug");
 
+var hasNativeURL = typeof URL !== undefined;
+
 // Create handlers that pass events from native requests
 var events = ["abort", "aborted", "connect", "error", "socket", "timeout"];
 var eventHandlers = Object.create(null);
@@ -15,12 +17,12 @@ events.forEach(function (event) {
   };
 });
 
+// Error types with codes
 var InvalidUrlError = createErrorType(
   "ERR_INVALID_URL",
   "Invalid URL",
   TypeError
 );
-// Error types with codes
 var RedirectionError = createErrorType(
   "ERR_FR_REDIRECTION_FAILURE",
   "Redirected request failed"
@@ -426,7 +428,7 @@ RedirectableRequest.prototype._processResponse = function (response) {
     url.format(Object.assign(currentUrlParts, { host: currentHost }));
 
   // Determine the URL of the redirection
-  var redirectUrl = url.resolve(currentUrl, location);
+  var redirectUrl = resolveUrl(location, currentUrl);
 
   // Create the redirected request
   debug("redirecting to", redirectUrl);
@@ -494,7 +496,7 @@ function wrap(protocols) {
         }
         input = parsed;
       }
-      else if (URL && (input instanceof URL)) {
+      else if (hasNativeURL && (input instanceof URL)) {
         input = urlToOptions(input);
       }
       else {
@@ -538,9 +540,15 @@ function wrap(protocols) {
   return exports;
 }
 
-/* istanbul ignore next */
 function noop() { /* empty */ }
 
+function resolveUrl(relative, base) {
+  return !hasNativeURL ?
+    /* istanbul ignore next */
+    url.resolve(base, relative) :
+    (new URL(relative, base)).href;
+}
+
 // from https://github.com/nodejs/node/blob/master/lib/internal/url.js
 function urlToOptions(urlObject) {
   var options = {

test/test.js

@@ -312,23 +312,6 @@ describe("follow-redirects", function () {
       });
   });
 
-  it("emits an error when url.resolve fails", function () {
-    app.get("/a", redirectsTo("/b"));
-    var urlResolve = url.resolve;
-    url.resolve = function () {
-      throw new Error();
-    };
-
-    return server.start(app)
-      .then(asPromise(function (resolve) {
-        http.get("http://localhost:3600/a").on("error", resolve);
-      }))
-      .then(function (error) {
-        url.resolve = urlResolve;
-        assert.equal(error.code, "ERR_FR_REDIRECTION_FAILURE");
-      });
-  });
-
   it("emits an error when the request fails for another reason", function () {
     app.get("/a", function (req, res) {
       res.socket.write("HTTP/1.1 301 Moved Permanently\r\n");