Typed arrays

[linlexing]

When can support Typed arrays?

[stevenh]

Do you have an example of what your trying to do?

[linlexing]

"Typed Array" is good and consume less memory than the "array " performance. "Typed Array" for reading and writing the file contents , as well as for data encryption and decryption.

// From a length
var uint8 = new Uint8Array(2);
uint8[0] = 42;
console.log(uint8[0]); // 42
console.log(uint8.length); // 2
console.log(uint8.BYTES_PER_ELEMENT); // 1

// From an array
var arr = new Uint8Array([21,31]);
console.log(arr[1]); // 31

// From another TypedArray
var x = new Uint8Array([21, 31]);
var y = new Uint8Array(x);
console.log(y[0]); // 21

// From an ArrayBuffer
var buffer = new ArrayBuffer(8);
var z = new Uint8Array(buffer, 1, 4);

[stevenh]

Apart from the BYTES_PER_ELEMENT, that should just work.

For the passing arrays in you'll need: #108

[boomshroom]

undefined ReferenceError: Float32Array is not defined

[ble]

References:
MDN: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Typed_arrays
Relevant section from Draft ECMA-262 6th Edition (April 3, 2015): http://people.mozilla.org/~jorendorff/es6-draft.html#sec-typedarray-objects

[robertkrimen]

I thought about this briefly before. It would be nice to have with Go's natives types, but I don't know of a straightforward way (leveraging Go) to present "typed views" of the same data.

[ble]

There is a standard library way of treating arbitrary bytes as a sequence of fixed-size values: http://golang.org/pkg/encoding/binary/#Read
http://golang.org/pkg/encoding/binary/#Write

It seems designed for bulk transform, not for providing a typed view of bytes. It might not perform very well if it gets called repeatedly, as you'd want to do for providing this interface. Docs for the package say "This package favors simplicity over efficiency."

There's always the package unsafe way, too.

[3dseals]

I got the error:
'Uint8Array' is not defined
'ArrayBuffer' is not defined
when require github.com/dcodeIO/ProtoBuf.js
I thought slices can be converted toArrayBuffer
Please refer to:

Go type	JavaScript type	Conversions back to interface{}
bool	Boolean	bool
integers and floats	Number	float64
string	String	string
[]int8	Int8Array	[]int8
[]int16	Int16Array	[]int16
[]int32, []int	Int32Array	[]int
[]uint8	Uint8Array	[]uint8
[]uint16	Uint16Array	[]uint16
[]uint32, []uint	Uint32Array	[]uint
[]float32	Float32Array	[]float32
[]float64	Float64Array	[]float64
all other slices	Array	[]interface{}
arrays	see slice type	see slice type
functions	Function	func(...interface{}) *js.Object
time.Time	Date	time.Time
-	instanceof Node	*js.Object
maps, structs	instanceof Object	map[string]interface{}

form gopherjs

by the way When can we use the ArrayBuffer

[boomshroom]

A little off topic, but Int32Array always gets converted to a []int? Even on a 64 bit machine where int means int64?

[hochhaus]

@stevenh Does your comment mean that typed arrays are currently implemented in otto?

When I try to to do something simple with types arrays (eg: var uint8 = new Uint8Array(2);) I receive a ReferenceError: 'Uint8Array' is not defined error.

[hochhaus]

Looking at the code a bit I'm reasonably confident that no attempt has been made to implement typed arrays. Could this limitation be documented in the caveat-emptor section of the README?

[deoxxa]

Typed Arrays aren't part of ES5, and I don't think we need to start listing all the ES6 features otto doesn't support.

[hochhaus]

That is fair, how about listing that otto targets ES5 then?

Typed arrays are relatively ubiquitous at this point (more so than much of ES6) so this seems like it might be a common pitfall.

[deoxxa]

Yep, fair call. I actually thought it was listed clearly already, but I appear to be mistaken! I'd happily merge a change to make this more obvious in the readme and the inline docs - could you put that in for me, @hochhaus?

[hochhaus]

Thanks @deoxxa. Change #216 sent.

[stevenh]

Typed arrays are part of ES6 so not currently supported, but it should be possible to do.