Core: suspend auctions during prerendering

src/prebid.js

@@ -569,13 +569,17 @@ pbjsInstance.requestBids = (function() {
     })
   }, 'requestBids');
 
-  return wrapHook(delegate, function requestBids(req = {}) {
+  return wrapHook(delegate, delayIfPrerendering(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.
 
+    // Note that we delay this when prerendering because in some configurations requestBids may happen outside of
+    // pbjs.que (e.g. NPM consumers).
+
     // 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]);
 
@@ -584,7 +588,7 @@ 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 } = {}) {
@@ -1018,16 +1022,36 @@ function processQueue(queue) {
   });
 }
 
+/**
+ * Returns a wrapper around fn that delays execution until the page if activated, if it was prerendered.
+ * https://developer.chrome.com/docs/web-platform/prerender-pages
+ */
+function delayIfPrerendering(fn) {
+  return function () {
+    if (document.prerendering && !(config.getConfig('allowPrerendering') || getGlobal().allowPrerendering)) {
+      const that = this;
+      const args = Array.from(arguments);
+      return new Promise((resolve) => {
+        document.addEventListener('prerenderingchange', () => {
+          logInfo(`Auctions are suspended while page is prerendering. Set $$PREBID_GLOBAL$$.allowPrerendering = true to allow auctions during prerendering.`)
+          resolve(fn.apply(that, args))
+        }, {once: true})
+      })
+    } else {
+      return Promise.resolve(fn.apply(this, arguments));
+    }
+  }
+}
 /**
  * @alias module:pbjs.processQueue
  */
-pbjsInstance.processQueue = function () {
+pbjsInstance.processQueue = delayIfPrerendering(function () {
   pbjsInstance.que.push = pbjsInstance.cmd.push = quePush;
   insertLocatorFrame();
   hook.ready();
   processQueue(pbjsInstance.que);
   processQueue(pbjsInstance.cmd);
-};
+});
 
 /**
  * @alias module:pbjs.triggerBilling

test/spec/unit/pbjs_api_spec.js

@@ -244,14 +244,81 @@ 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('when document 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 process queue only after prerenderingchange event', async () => {
+            pushToQueue();
+            $$PREBID_GLOBAL$$.processQueue();
+            pushToQueue();
+            expect(ran).to.be.false;
+            prerenderingDone();
+            expect(ran).to.be.true;
+          });
+
+          Object.entries({
+            'setConfig({allowPrerendering: true})': {
+              setup() {
+                $$PREBID_GLOBAL$$.setConfig({allowPrerendering: true});
+              },
+              teardown() {
+                $$PREBID_GLOBAL$$.setConfig({allowPrerendering: false});
+              }
+            },
+            '$$PREBID_GLOBAL$$.allowPrerendering = true': {
+              setup() {
+                $$PREBID_GLOBAL$$.allowPrerendering = true;
+              },
+              teardown() {
+                delete $$PREBID_GLOBAL$$.allowPrerendering;
+              }
+            }
+          }).forEach(([t, {setup, teardown}]) => {
+            describe(`with ${t}`, () => {
+              beforeEach(setup);
+              afterEach(teardown);
+              it('should process immediately', () => {
+                pushToQueue();
+                $$PREBID_GLOBAL$$.processQueue();
+                expect(ran).to.be.true;
+              })
+            })
+          })
+        })
       })
-    })
+    });
   })
 
   describe('and global adUnits', () => {