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WebAssembly.memory

The WebAssembly.Memory object 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.

Constructor

WebAssembly.Memory()
Creates a new Memory object.

Instance properties

Memory.prototype.buffer
An accessor property that returns the buffer contained in the memory.

Instance methods

Memory.prototype.grow()
Increases the size of the memory instance by a specified number of WebAssembly pages (each one is 64KB in size).

Examples

Creating a new Memory object

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 compatibilityUpdate compatibility data on GitHub

Desktop
Chrome Edge Firefox Internet Explorer Opera Safari
Memory 57 16 52
52
Disabled in the Firefox 52 Extended Support Release (ESR).
No 44 11
Memory() constructor 57 16 52
52
Disabled in the Firefox 52 Extended Support Release (ESR).
No 44 11
buffer 57 16 52
52
Disabled in the Firefox 52 Extended Support Release (ESR).
No 44 11
grow 57 16 52
52
Disabled in the Firefox 52 Extended Support Release (ESR).
No 44 11
Mobile
Android webview Chrome for Android Firefox for Android Opera for Android Safari on iOS Samsung Internet
Memory 57 57 52
52
Disabled in the Firefox 52 Extended Support Release (ESR).
43 11 7.0
Memory() constructor 57 57 52
52
Disabled in the Firefox 52 Extended Support Release (ESR).
43 11 7.0
buffer 57 57 52
52
Disabled in the Firefox 52 Extended Support Release (ESR).
43 11 7.0
grow 57 57 52
52
Disabled in the Firefox 52 Extended Support Release (ESR).
43 11 7.0
Server
Node.js
Memory 8.0.0
Memory() constructor 8.0.0
buffer 8.0.0
grow 8.0.0

See also

© 2005–2018 Mozilla Developer Network and individual contributors.
Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.
https://wiki.developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WebAssembly/Memory