Asynchronously loads the given URL as JSON. Returns a promise that will resolve to a JSON object once loaded, or reject if the URL failed to load. The data is loaded using XMLHttpRequest, which means that in order to make requests to another origin, the server must have Cross-Origin Resource Sharing (CORS) headers enabled. This function adds 'Accept: application/json,*/*;q=0.01' to the request headers, if not already specified.
||String||The URL to request.|
||Object||optional HTTP headers to send with the request. 'Accept: application/json,*/*;q=0.01' is added to the request headers automatically if not specified.|
||Request||optional The request object. Intended for internal use only.|
a promise that will resolve to the requested data when loaded. Returns undefined if
request.throttleis true and the request does not have high enough priority.