Angular HttpErrorResponse blob error response doesn't trigger FileReader

When requesting a file and an error is returned I get the error response in a Blob instance

error: Blob {size: 97, type: 'application/json'}
headers: HttpHeaders {normalizedNames: Map(0), lazyUpdate: null, lazyInit: ƒ}
message: "Http failure response for redacted: 404 OK"
name: "HttpErrorResponse"
ok: false
status: 404
statusText: "OK"
url: "redacted"


Given that, I can't do my standard check in the error property for a message. I'm attempting to read the response as the response itself is the correct format, just a blob:

if (requestError.type === 'application/json') {
console.log('start parsing');
const reader = new FileReader();
reader.onload = (event) => {
console.log(event);
console.log('reader.result', reader.result);
try {
requestError = JSON.parse(reader.result as string);
console.log('Parsed JSON response:', requestError);
} catch (e) {
console.log('Error parsing JSON response:', e);
}
}
return;
}


"start parsing" is fired but the onload event isn't. I've tried onloadend as well as setting the event trigger as reader.addEventListener('loadend', (event) => { but nothing inside the loading events fires. I'm checking the response I can confirm it's a blob and the response is in json.

Not sure why the FileReader event's are being triggered.

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