WebAssembly.Memory
The WebAssembly.Memory
object is a resizable ArrayBuffer
or SharedArrayBuffer
that holds the raw bytes of memory accessed by a WebAssembly.Instance
.
Both WebAssembly and JavaScript can create Memory
objects. If you want to access the memory created in JS from Wasm or vice versa, you can pass a reference to the memory from one side to the other.
Constructor
WebAssembly.Memory()
-
Creates a new
Memory
object.
Instance properties
Memory.prototype.buffer
Read only-
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 64KiB in size). Detaches the previous
buffer
.
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 snippet 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
.
js
const memory = new WebAssembly.Memory({
initial: 10,
maximum: 100,
});
The following example (see memory.html on GitHub, and view it live also) fetches and instantiates the loaded memory.wasm bytecode using the WebAssembly.instantiateStreaming()
function, while importing the memory created in the line above. It then stores some values in that memory, exports a function, and uses the exported function to sum those values.
js
const memory = new WebAssembly.Memory({
initial: 10,
maximum: 100,
});
WebAssembly.instantiateStreaming(fetch("memory.wasm"), {
js: { mem: memory },
}).then((obj) => {
const summands = new Uint32Array(memory.buffer);
for (let i = 0; i < 10; i++) {
summands[i] = i;
}
const sum = obj.instance.exports.accumulate(0, 10);
console.log(sum);
});
Another way to get a WebAssembly.Memory
object is to have it exported by a WebAssembly module. This memory can be accessed in the exports
property of the WebAssembly instance (after the memory is exported within the WebAssembly module). The following example imports a memory exported from WebAssembly with the name memory
, and then prints out the first element of the memory, interpreted as an Uint32Array
.
js
WebAssembly.instantiateStreaming(fetch("memory.wasm")).then((obj) => {
const values = new Uint32Array(obj.instance.exports.memory.buffer);
console.log(values[0]);
});
Creating a shared memory
By default, WebAssembly memories are unshared. You can create a shared memory from JavaScript by passing shared: true
in the constructor's initialization object:
js
const memory = new WebAssembly.Memory({
initial: 10,
maximum: 100,
shared: true,
});
This memory's buffer
property will return a SharedArrayBuffer
.
Specifications
Specification |
---|
WebAssembly JavaScript Interface # memories |
Browser compatibility
BCD tables only load in the browser