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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.
Syntax
var myMemory = 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. In general, most WebAssembly modules shouldn't need to set amaximum
.
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.
Memory
instances
All Memory
instances inherit from the Memory()
constructor's prototype object — this can be modified to affect all Memory
instances.
Instance properties
Memory.prototype.constructor
- Returns the function that created this object's instance. By default this is the
WebAssembly.Memory()
constructor. 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
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); });
Specifications
Specification | Status | Comment |
---|---|---|
WebAssembly JavaScript Interface The definition of 'Memory' in that specification. |
Working Draft | Initial draft definition. |
Browser compatibility
Desktop | Mobile | Server | ||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Basic support | 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 | Edge Mobile
Full support
Yes
| Firefox Android
Full support
52
| Opera Android ? | Safari iOS Full support 11 | Samsung Internet Android Full support 7.0 | nodejs Full support 8.0.0 |
buffer | 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 | Edge Mobile
Full support
Yes
| Firefox Android
Full support
52
| Opera Android ? | Safari iOS Full support 11 | Samsung Internet Android Full support 7.0 | nodejs Full support 8.0.0 |
grow | 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 | Edge Mobile
Full support
Yes
| Firefox Android
Full support
52
| Opera Android ? | Safari iOS Full support 11 | Samsung Internet Android Full support 7.0 | nodejs Full support 8.0.0 |
prototype | 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 | Edge Mobile
Full support
Yes
| Firefox Android
Full support
52
| Opera Android ? | Safari iOS Full support 11 | Samsung Internet Android Full support 7.0 | nodejs Full support 8.0.0 |
Legend
- Full support
- Full support
- No support
- No support
- Compatibility unknown
- Compatibility unknown
- See implementation notes.
- See implementation notes.
- User must explicitly enable this feature.
- User must explicitly enable this feature.