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Blob.slice

The Blob.slice() method is used to create a new Blob object containing the data in the specified range of bytes of the source Blob.

Note: Be aware that the slice() method has vendor prefixes on some browsers and versions: blob.mozSlice() for Firefox 12 and earlier and blob.webkitSlice() in Safari. An old version of the slice() method, without vendor prefixes, had different semantics, and is obsolete.

Syntax

var blob = instanceOfBlob.slice([start [, end [, contentType]]]);

Parameters

start Optional: An index into the Blob indicating the first byte to include in the new Blob. If you specify a negative value, it's treated as an offset from the end of the string toward the beginning. For example, -10 would be the 10th from last byte in the Blob. The default value is 0. If you specify a value for start that is larger than the size of the source Blob, the returned Blob has size 0 and contains no data.
end Optional: An index into the Blob indicating the first byte that will *not* be included in the new Blob (i.e. the byte exactly at this index is not included). If you specify a negative value, it's treated as an offset from the end of the string toward the beginning. For example, -10 would be the 10th from last byte in the Blob. The default value is size.
contentType Optional: The content type to assign to the new Blob; this will be the value of its type property. The default value is an empty string.

Return value

A new Blob object containing the specified data from the source Blob.

Specifications

Specification	Status	Comment
File API The definition of 'Blob.slice()' in that specification.	Working Draft	Initial definition

Browser compatibility

Feature	Chrome	Edge	Firefox (Gecko)	Internet Explorer	Opera	Safari (WebKit)
Basic support	10 webkit [1] 21	(Yes)	5 moz [1] 13 [2]	10	12 [1]	5.1 webkit [3]

Feature	Android	Edge	Firefox Mobile (Gecko)	IE Phone	Opera Mobile	Safari Mobile
Basic support	?	(Yes)	13.0 (13.0)	?	?	?

[1] The slice() method had initially taken length as the second argument to indicate the number of bytes to include in the new Blob. If you specified values such that start + length exceeded the size of the source Blob, the returned Blob contained data from the start index to the end of the source Blob. That version of the slice() was implemented in Firefox 4, WebKit, and Opera 11.10. However, since that syntax is differed from Array.slice() and String.slice(), Gecko and WebKit removed support and added support for the new syntax as Blob.slice()/Blob.webkitSlice.

[2] Prior to Gecko 12.0 (Firefox 12.0 / Thunderbird 12.0 / SeaMonkey 2.9), there was a bug that affected the behavior of Blob.slice(); it did not work for start and end positions outside the range of signed 64-bit values; it has now been fixed to support unsigned 64-bit values.