Angular can make many assumptions about its event handlers. As a result
the bookkeeping for native addEventListener is significantly cheaper
than Zone's addEventLister which can't make such assumptions.
This change bypasses the Zone's addEventListener if present and always
uses the native addEventHandler. As a result registering event listeners
is about 3 times faster.
PR Close#18107
HttpClient is an evolution of the existing Angular HTTP API, which exists
alongside of it in a separate package, @angular/common/http. This structure
ensures that existing codebases can slowly migrate to the new API.
The new API improves significantly on the ergonomics and features of the legacy
API. A partial list of new features includes:
* Typed, synchronous response body access, including support for JSON body types
* JSON is an assumed default and no longer needs to be explicitly parsed
* Interceptors allow middleware logic to be inserted into the pipeline
* Immutable request/response objects
* Progress events for both request upload and response download
* Post-request verification & flush based testing framework
