The WebAssembly.Memory()
constructor creates a new Memory
object whose buffer
property is a resizable ArrayBuffer
or SharedArrayBuffer
that holds the raw bytes of memory accessed by a WebAssembly Instance
.
A memory created by JavaScript or in WebAssembly code will be accessible and mutable from both JavaScript and WebAssembly.
Syntax
new WebAssembly.Memory(memoryDescriptor);
Parameters
- memoryDescriptor
- An object that can contain the following members:
- initial
- The initial size of the WebAssembly Memory, in units of WebAssembly pages.
- maximum Optional
- The maximum size the WebAssembly Memory is allowed to grow to, in units of WebAssembly pages. When present, the
maximum
parameter acts as a hint to the engine to reserve memory up front. However, the engine may ignore or clamp this reservation request. Unshared WebAssembly memories don't need to set amaximum
, but shared memories do. - shared Optional
- A boolean value that defines whether the memory is a shared memory or not. If set to
true
, it is a shared memory. The default isfalse
.
Note: A WebAssembly page has a constant size of 65,536 bytes, i.e., 64KiB.
Exceptions
- If
memoryDescriptor
is not of type object, aTypeError
is thrown. - If
maximum
is specified and is smaller thaninitial
, aRangeError
is thrown.
Examples
Creating a new Memory instance
There are two ways to get a WebAssembly.Memory
object. The first way is to construct it from JavaScript. The following example creates a new WebAssembly Memory instance with an initial size of 10 pages (640KiB), and a maximum size of 100 pages (6.4MiB). Its buffer
property will return an ArrayBuffer
.
var memory = new WebAssembly.Memory({initial:10, maximum:100});
The second way to get a WebAssembly.Memory
object is to have it exported by a WebAssembly module. The following example (see memory.html on GitHub, and view it live also) fetches and instantiates the loaded memory.wasm byte code using the WebAssembly.instantiateStreaming()
method, while importing the memory created in the line above. It then stores some values in that memory, then exports a function and uses it to sum some values.
WebAssembly.instantiateStreaming(fetch('memory.wasm'), { js: { mem: memory } }) .then(obj => { var i32 = new Uint32Array(memory.buffer); for (var i = 0; i < 10; i++) { i32[i] = i; } var sum = obj.instance.exports.accumulate(0, 10); console.log(sum); });
Creating a shared memory
By default, WebAssembly memories are unshared. You can create a shared memory by passing shared: true
in the constructor's initialization object:
let memory = new WebAssembly.Memory({initial:10, maximum:100, shared:true});
This memory's buffer
property will return a SharedArrayBuffer
.
Specifications
Specification |
---|
WebAssembly JavaScript Interface The definition of 'Memory' in that specification. |
Browser compatibility
Desktop | Mobile | Server | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Memory() constructor | Chrome Full support 57 | Edge Full support 16 | Firefox
Full support
52
| IE No support No | Opera Full support 44 | Safari Full support 11 | WebView Android Full support 57 | Chrome Android Full support 57 | Firefox Android
Full support
52
| Opera Android Full support 43 | Safari iOS Full support 11 | Samsung Internet Android Full support 7.0 | nodejs Full support 8.0.0 |
shared flag | Chrome Full support 74 | Edge Full support 79 | Firefox Full support 78 | IE No support No | Opera Full support 62 | Safari No support No | WebView Android No support No | Chrome Android No support No | Firefox Android No support No | Opera Android No support No | Safari iOS No support No | Samsung Internet Android No support No | nodejs Full support 12.0.0 |
Legend
- Full support
- Full support
- No support
- No support
- See implementation notes.
- See implementation notes.