For a variety of reasons, collections of entities are often split into pages and each page is returned with a URL to the next page. Sometimes, page granularity provided by the API does not match the requirements of the consumer. PageIterator simplifies consuming of paged collections.
asyncfunctioncallingPattern(){try{// Makes request to fetch mails list. Which is expected to have multiple pages of data.letresponse: PageCollection=awaitclient.api("/me/messages").get();// A callback function to be called for every item in the collection. This call back should return boolean indicating whether not to continue the iteration process.letcallback: PageIteratorCallback=(data)=>{console.log(data);returntrue;};// Creating a new page iterator instance with client a graph client instance, page collection response from request and callbackletpageIterator=newPageIterator(client,response,callback);// This iterates the collection until the nextLink is drained out.awaitpageIterator.iterate();}catch(e){throwe;}}// Populating custom size pages if the api restricts to some maximum size. Lazy loading more data on user prompt or something, stop and resume will do the trick.asyncfunctioncustomSize(){try{letresponse: PageCollection=awaitclient.api("/me/messages").get();letsize=1000;letcount=0;letcallback: PageIteratorCallback=(data)=>{console.log(data);count++;if(count===size){count=0;returnfalse;}returntrue;};letpageIterator=newPageIterator(client,response,callback);// This stops iterating over for 1000 entities.awaitpageIterator.iterate();// Resuming will do start from where it left off and iterate for next 1000 entities.// Check and resume is likely to be called in any user interaction requiring to load more data.if(!pageIterator.isComplete()){awaitpageIterator.resume();}}catch(e){throwe;}}