They aim to improve code readability.
Since they are defined by `const enum` they have zero runtime performance impact
over just using constant literals.
Fixes#23543
PR Close#23548
Before this change, when trying to load a JSONP script that calls the JSONP callback inside a
microtask, it will fail in Internet Explorer 11 and EdgeHTML. This commit changes the onLoad cleanup
to be queued after the loaded endpoint executed any potential microtask itself. This ensures that
the aforementioned browsers will first evaluate the loaded script calling the JSONP callback and
only then run the cleanup inside onLoad.
Fixes#39496
PR Close#39512
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
