syntax:

buffer.size

description:

The size of the Buffer object. This property may be assigned to, such as foo.size = 5. If a user changes the size of the buffer to something larger, then it is filled with NULL bytes. If the user sets the Buffer size to a value smaller than the current position of the Buffer cursor, then the cursor is moved to the end of the new buffer.

see:

Buffer cursor

example:

var n = buffer.size;