Node fs.readFileSync returns a uInt8 array instead of raw buffer array?

Question

why is this:

var myArrayBuffer = fs.readFileSync(file, null)

returning an uInt8 array instead of a just a arrayBuffer? why does this seem to work?

var myArrayBuffer = fs.readFileSync(file, null).buffer;
var myAArray = new Uint16Array( myArrayBuffer.slice(266,(sizeofArray*sizeOfArrayElement));

Why would the fs.readFile parse my file into a uInt8 array? Makes no sense, the file has a bunch of different datatypes that are not 1 byte long.

raina77ow · Accepted Answer · 2017-05-03 20:28:30Z

6

Because since v3.0.0 Buffer class inherits from Uint8Array class. Quoting the doc:

Buffer instances are also Uint8Array instances. However, there are subtle incompatibilities with the TypedArray specification in ECMAScript 2015. For example, while ArrayBuffer#slice() creates a copy of the slice, the implementation of Buffer#slice() creates a view over the existing Buffer without copying, making Buffer#slice() far more efficient. [...]

It is possible to create a new Buffer that shares the same allocated memory as a TypedArray instance by using the TypeArray object's .buffer property.

... which is exactly what's done in your example.

edited May 3, 2017 at 20:28

answered May 3, 2017 at 20:08

raina77ow

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4 Comments

LrakWortep Over a year ago

But why would someone ever need the uInt8Array? You read a file directly into a buffer and deal with bytes? If you read in a binary file the chance of it being all being uInt8 seems slim and just adds overhead, and in my case confusion and frustration.

raina77ow Over a year ago

Not sure what you mean here. Yes, Buffer is also Uint8Array - but you don't have to use it as former.

LrakWortep Over a year ago

I'm confused too;) buffer doesnt seem to also be a uint8Array because the uint8Array.slice(266,length) gives me the Uint8array Indexes so its twice as much, where the buffer slice slices single bytes. Just seems like added overhead

raina77ow Over a year ago

Yes, and that's also mentioned in the docs. Inheritance in this case means also overriding some methods' behaviour.

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