In Javascript, when opening a file via an “input file” button, is the entire file read into memory

In javascript, when opening a file via a button returns a Blob object (e.g. blob1).
I can then get the actual data of the blob via blob1ArrayBuffer = blob1.arrayBuffer();

When the Blob object (e.g. blob1) is created, does it load all the bytes into memory?
Or does it just returns the address so that later the actual bytes can be read via blob1.arrayBuffer() ?