WebAssembly.Memory() constructor
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
Browser compatibility
BCD tables only load in the browser