[File API] About Partial Blob Data

Hi all,

Reading the File API, it is not clear to me what the behavior is when 
reading partial Blob data. The spec says:
" Partial Blob data is the part of the |File| 
<http://dev.w3.org/2006/webapi/FileAPI/#dfn-file> or |Blob| 
<http://dev.w3.org/2006/webapi/FileAPI/#dfn-Blob> that has been read 
into memory /currently/;
when processing the read method 
<http://dev.w3.org/2006/webapi/FileAPI/#read-methods> |readAsText| 
<http://dev.w3.org/2006/webapi/FileAPI/#dfn-readAsText>, partial Blob 
data is a |DOMString| that is incremented as more bytes are |loaded| (a 
portion of the |total|) [ProgressEvents 
and when processing |readAsArrayBuffer| 
<http://dev.w3.org/2006/webapi/FileAPI/#dfn-readAsArrayBuffer> partial 
Blob data is an |ArrayBuffer| [TypedArrays 
<http://dev.w3.org/2006/webapi/FileAPI/#TypedArrays>] object consisting 
of the bytes |loaded| so far (a portion of the |total|)[ProgressEvents 
<http://dev.w3.org/2006/webapi/FileAPI/#ProgressEvents>]. "

Does this mean that the result object is the same or it is a new object 
each time there is a progress event ? In the case of a DOMString, it 
could be the same object incremented but if it is an ArrayBuffer, since 
it is immutable, it cannot be incremented. So in the case the final 
length of the Blob is not known yet (e.g. chunked XHR), result has to be 
a new object each time. Am I wrong here? If not, could you clarify the 
spec ?


Cyril Concolato
Maître de Conférences/Associate Professor
Groupe Multimedia/Multimedia Group
Telecom ParisTech
46 rue Barrault
75 013 Paris, France

Received on Thursday, 17 January 2013 09:56:45 UTC