fix: Proxy route.params onto the request instead of mutating req

packages/@pollyjs/core/src/-private/request.js

@@ -34,9 +34,6 @@ export default class PollyRequest {
     */
     this.action = null;
 
-    // This will be overridden by the route when a method is invoked
-    this.params = {};
-
     // Lookup the associated route for this request
     this[ROUTE] = polly.server.lookup(this.method, this.url);
   }

packages/@pollyjs/core/src/server/route.js

@@ -2,17 +2,18 @@ import Handler from './handler';
 
 async function invoke(fn, route, req, ...args) {
   if (typeof fn === 'function') {
-    const params = req.params;
+    const proxyReq = new Proxy(req, {
+      get(source, prop) {
+        if (prop === 'params') {
+          // Set the request's params to given route's matched params
+          return route.params;
+        }
 
-    // Set the request's params to given route's matched params
-    req.params = route.params || {};
+        return source[prop];
+      }
+    });
 
-    const result = await fn(req, ...args);
-
-    // Reset the params object to what it was before
-    req.params = params;
-
-    return result;
+    return await fn(proxyReq, ...args);
   }
 }
 

packages/@pollyjs/core/tests/integration/persisters-test.js

@@ -105,6 +105,25 @@ describe('Integration | Persisters', function() {
         expect(savedRecording.entries[entryKeys[0]].length).to.equal(2);
         expect(savedRecording.entries[entryKeys[1]].length).to.equal(1);
       });
+
+      it('should emit beforePersist', async function() {
+        const { persister, server } = this.polly;
+        let beforePersistCalled = false;
+
+        server.get('/api/db/:id').on('beforePersist', (req /*, res*/) => {
+          expect(req.params.id).to.equal('foo');
+          expect(beforePersistCalled).to.be.false;
+          beforePersistCalled = true;
+        });
+
+        this.polly.record();
+
+        await this.fetch('/api/db/foo');
+        expect(beforePersistCalled).to.be.false;
+
+        await persister.persist();
+        expect(beforePersistCalled).to.be.true;
+      });
     });
 
     describe(`${name} | recordFailedRequests set to false`, function() {