The WebAssembly.Memory()
constructor creates a new Memory
object which is a resizable ArrayBuffer 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.
var myMemory = new WebAssembly.Memory(memoryDescriptor);
maximum
parameter acts as a hint to the engine to reserve memory up front. However, the engine may ignore or clamp this reservation request. In general, most WebAssembly modules shouldn't need to set a maximum
.Note: A WebAssembly page has a constant size of 65,536 bytes, i.e., 64KiB.
memoryDescriptor
is not of type object, a TypeError
is thrown.maximum
is specified and is smaller than initial
, a RangeError
is thrown.Memory
instancesAll Memory
instances inherit from the Memory()
constructor's prototype object — this can be modified to affect all Memory
instances.
Memory.prototype.constructor
WebAssembly.Memory()
constructor.Memory.prototype.buffer
Memory.prototype.grow()
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).
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); });
Specification | Status | Comment |
---|---|---|
WebAssembly JavaScript Interface The definition of 'Memory' in that specification. | Working Draft | Initial draft definition. |
Desktop | ||||||
---|---|---|---|---|---|---|
Chrome | Edge | Firefox | Internet Explorer | Opera | Safari | |
Basic support | 57 | 16 | 52
|
No | 44 | 11 |
buffer |
57 | 16 | 52
|
No | 44 | 11 |
grow |
57 | 16 | 52
|
No | 44 | 11 |
prototype |
57 | 16 | 52
|
No | 44 | 11 |
Mobile | |||||||
---|---|---|---|---|---|---|---|
Android webview | Chrome for Android | Edge Mobile | Firefox for Android | Opera for Android | iOS Safari | Samsung Internet | |
Basic support | 57 | 57 | Yes
|
52
|
? | 11 | 7.0 |
buffer |
57 | 57 | Yes
|
52
|
? | 11 | 7.0 |
grow |
57 | 57 | Yes
|
52
|
? | 11 | 7.0 |
prototype |
57 | 57 | Yes
|
52
|
? | 11 | 7.0 |
Server | |
---|---|
Node.js | |
Basic support | 8.0.0 |
buffer |
8.0.0 |
grow |
8.0.0 |
prototype |
8.0.0 |
© 2005–2018 Mozilla Developer Network and individual contributors.
Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WebAssembly/Memory