A Blob object represents a file-like object of immutable, raw data. Blobs
interface is based on Blob, inheriting blob functionality and expanding it to
support files on the user's system.
An easy way to construct a Blob is by invoking the Blob constuctor. Another
way is to use the slice() method to create a blob that contains a subset of
another blob's data.
The size, in bytes, of the data contained in the Blob object.
The slice is used to create a new Blob object containing the data in the specified
range of bytes of the source Blob.