Core: suspend auctions during prerendering

src/prebid.js

@@ -50,6 +50,7 @@ import {getHighestCpm} from './utils/reducers.js';
 import {ORTB_VIDEO_PARAMS, fillVideoDefaults, validateOrtbVideoFields} from './video.js';
 import { ORTB_BANNER_PARAMS } from './banner.js';
 import { BANNER, VIDEO } from './mediaTypes.js';
+import {delayIfPrerendering} from './utils/prerendering.js';
 import { newBidder } from './adapters/bidderFactory.js';
 
 const pbjsInstance = getGlobal();
@@ -570,13 +571,14 @@ pbjsInstance.requestBids = (function() {
     })
   }, 'requestBids');
 
-  return wrapHook(delegate, function requestBids(req = {}) {
+  return wrapHook(delegate, delayIfPrerendering(() => !config.getConfig('allowPrerendering'), function requestBids(req = {}) {
     // unlike the main body of `delegate`, this runs before any other hook has a chance to;
     // it's also not restricted in its return value in the way `async` hooks are.
 
     // if the request does not specify adUnits, clone the global adUnit array;
     // otherwise, if the caller goes on to use addAdUnits/removeAdUnits, any asynchronous logic
     // in any hook might see their effects.
+
     let adUnits = req.adUnits || pbjsInstance.adUnits;
     req.adUnits = (isArray(adUnits) ? adUnits.slice() : [adUnits]);
 
@@ -585,7 +587,7 @@ pbjsInstance.requestBids = (function() {
     req.defer = defer({promiseFactory: (r) => new Promise(r)})
     delegate.call(this, req);
     return req.defer.promise;
-  });
+  }));
 })();
 
 export const startAuction = hook('async', function ({ bidsBackHandler, timeout: cbTimeout, adUnits, ttlBuffer, adUnitCodes, labels, auctionId, ortb2Fragments, metrics, defer } = {}) {
@@ -1026,13 +1028,13 @@ function processQueue(queue) {
 /**
  * @alias module:pbjs.processQueue
  */
-pbjsInstance.processQueue = function () {
+pbjsInstance.processQueue = delayIfPrerendering(() => getGlobal().delayPrerendering, function () {
   pbjsInstance.que.push = pbjsInstance.cmd.push = quePush;
   insertLocatorFrame();
   hook.ready();
   processQueue(pbjsInstance.que);
   processQueue(pbjsInstance.cmd);
-};
+});
 
 /**
  * @alias module:pbjs.triggerBilling

src/utils/prerendering.js

@@ -0,0 +1,22 @@
+import {logInfo} from '../utils.js';
+
+/**
+ * Returns a wrapper around fn that delays execution until the page if activated, if it was prerendered and isDelayEnabled returns true.
+ * https://developer.chrome.com/docs/web-platform/prerender-pages
+ */
+export function delayIfPrerendering(isDelayEnabled, fn) {
+  return function () {
+    if (document.prerendering && isDelayEnabled()) {
+      const that = this;
+      const args = Array.from(arguments);
+      return new Promise((resolve) => {
+        document.addEventListener('prerenderingchange', () => {
+          logInfo(`Auctions were suspended while page was prerendering`)
+          resolve(fn.apply(that, args))
+        }, {once: true})
+      })
+    } else {
+      return Promise.resolve(fn.apply(this, arguments));
+    }
+  }
+}

test/spec/unit/pbjs_api_spec.js

@@ -244,14 +244,27 @@ describe('Unit: Prebid Module', function () {
     });
 
     ['cmd', 'que'].forEach(prop => {
-      it(`should patch ${prop}.push`, () => {
-        $$PREBID_GLOBAL$$[prop].push = false;
-        $$PREBID_GLOBAL$$.processQueue();
-        let ran = false;
-        $$PREBID_GLOBAL$$[prop].push(() => { ran = true; });
-        expect(ran).to.be.true;
+      describe(`using .${prop}`, () => {
+        let queue, ran;
+        beforeEach(() => {
+          ran = false;
+          queue = $$PREBID_GLOBAL$$[prop] = [];
+        });
+        after(() => {
+          $$PREBID_GLOBAL$$.processQueue();
+        })
+
+        function pushToQueue() {
+          queue.push(() => { ran = true });
+        }
+
+        it(`should patch .push`, () => {
+          $$PREBID_GLOBAL$$.processQueue();
+          pushToQueue();
+          expect(ran).to.be.true;
+        });
       })
-    })
+    });
   })
 
   describe('and global adUnits', () => {

test/spec/utils/prerendering_spec.js

@@ -0,0 +1,53 @@
+import {delayIfPrerendering} from '../../../src/utils/prerendering.js';
+
+describe('delayIfPrerendering', () => {
+  let sandbox, enabled, ran;
+  beforeEach(() => {
+    sandbox = sinon.sandbox.create();
+    enabled = true;
+    ran = false;
+  });
+
+  afterEach(() => {
+    sandbox.restore();
+  })
+
+  const delay = delayIfPrerendering(() => enabled, () => {
+    ran = true;
+  })
+
+  it('should not delay if page is not prerendering', () => {
+    delay();
+    expect(ran).to.be.true;
+  })
+
+  describe('when page is prerendering', () => {
+    before(() => {
+      if (!('prerendering' in document)) {
+        document.prerendering = null;
+        after(() => {
+          delete document.prerendering;
+        })
+      }
+    })
+    beforeEach(() => {
+      sandbox.stub(document, 'prerendering').get(() => true);
+    });
+    function prerenderingDone() {
+      document.dispatchEvent(new Event('prerenderingchange'));
+    }
+
+    it('should run fn only after prerenderingchange event', async () => {
+      delay();
+      expect(ran).to.be.false;
+      prerenderingDone();
+      expect(ran).to.be.true;
+    });
+
+    it('should not delay if not enabled', () => {
+      enabled = false;
+      delay();
+      expect(ran).to.be.true;
+    })
+  })
+})