Set FileReader to LOADING state while a read is in progress

[durvesh1992]

Summary

FileReader's readAsText / readAsDataURL / readAsArrayBuffer go straight from EMPTY to DONE — they never set readyState to LOADING. Two consequences:

1. readyState is never observably LOADING during a read (it should be, per the W3C FileReader spec).

2. abort() is dead during a read. Its body only emits events when the reader is mid-read:

   abort() {
     this._aborted = true;
     // only call onreadystatechange if there is something to abort, as per spec
     if (this._readyState !== EMPTY && this._readyState !== DONE) {
       this._reset();
       this._setReadyState(DONE);
     }
     this._reset();
   }

   Because a read never sets LOADING, readyState is still EMPTY when abort() runs, so the guard is false and no abort/loadend events are dispatched — even though the method is written specifically to handle that case.

Fix

Set the LOADING state when each read starts (via the existing _setReadyState helper, which also fires readystatechange). This makes readyState correct during a read and makes abort() during a read dispatch abort/loadend as its own code already anticipates.

Test plan

Added tests to Libraries/Blob/__tests__/FileReader-test.js:

• readyState is LOADING synchronously after a read starts.
• abort() during a read dispatches abort and loadend.

Both fail before this change and pass after; the existing read tests and the full Blob test suite still pass (20/20). ESLint clean on the changed files.

Changelog:

[General] [Fixed] - Set FileReader readyState to LOADING during a read so abort() correctly emits abort/loadend

[meta-codesync]

@Abbondanzo has imported this pull request. If you are a Meta employee, you can view this in D110191434.

[meta-codesync]

@Abbondanzo merged this pull request in c00813c.