WebAssembly
Baseline
Widely available
*
This feature is well established and works across many devices and browser versions. It’s been available across browsers since October 2017.
* Some parts of this feature may have varying levels of support.
The WebAssembly JavaScript object acts as the namespace for all WebAssembly-related functionality.
Unlike most other global objects, WebAssembly is not a constructor (it is not a function object). You can compare it to Math, which is also a namespace object for mathematical constants and functions, or to Intl which is the namespace object for internationalization constructors and other language-sensitive functions.
Description
The primary uses for the WebAssembly object are:
- Loading WebAssembly code, using the
WebAssembly.instantiate()function. - Creating new memory and table instances via the
WebAssembly.Memory()/WebAssembly.Table()constructors. - Providing facilities to handle errors that occur in WebAssembly via the
WebAssembly.CompileError()/WebAssembly.LinkError()/WebAssembly.RuntimeError()constructors.
Interfaces
WebAssembly.CompileError-
Indicates an error during WebAssembly decoding or validation.
WebAssembly.Global-
Represents a global variable instance, accessible from both JavaScript and importable/exportable across one or more
WebAssembly.Moduleinstances. This allows dynamic linking of multiple modules. WebAssembly.Instance-
Is a stateful, executable instance of a
WebAssembly.Module WebAssembly.LinkError-
Indicates an error during module instantiation (besides traps from the start function).
WebAssembly.Memory-
An object whose
bufferproperty is a resizableArrayBufferthat holds the raw bytes of memory accessed by a WebAssemblyInstance. WebAssembly.Module-
Contains stateless WebAssembly code that has already been compiled by the browser and can be efficiently shared with Workers, and instantiated multiple times.
WebAssembly.RuntimeError-
Error type that is thrown whenever WebAssembly specifies a trap.
WebAssembly.Table-
An array-like structure representing a WebAssembly Table, which stores references, such as function references.
WebAssembly.Tag-
An object that represents a type of WebAssembly exception.
WebAssembly.Exception-
A WebAssembly exception object that can be thrown, caught, and rethrown both within and across WebAssembly/JavaScript boundaries.
Static methods
WebAssembly.compile()-
Compiles a
WebAssembly.Modulefrom WebAssembly binary code, leaving instantiation as a separate step. WebAssembly.compileStreaming()-
Compiles a
WebAssembly.Moduledirectly from a streamed underlying source, leaving instantiation as a separate step. WebAssembly.instantiate()-
The primary API for compiling and instantiating WebAssembly code, returning both a
Moduleand its firstInstance. WebAssembly.instantiateStreaming()-
Compiles and instantiates a WebAssembly module directly from a streamed underlying source, returning both a
Moduleand its firstInstance. WebAssembly.validate()-
Validates a given typed array of WebAssembly binary code, returning whether the bytes are valid WebAssembly code (
true) or not (false).
Examples
Stream a Wasm module then compile and instantiate it
The following example (see our instantiate-streaming.html demo on GitHub, and view it live also) directly streams a Wasm module from an underlying source then compiles and instantiates it, the promise fulfilling with a ResultObject. Because the instantiateStreaming() function accepts a promise for a Response object, you can directly pass it a fetch() call, and it will pass the response into the function when it fulfills.
const importObject = {
my_namespace: { imported_func: (arg) => console.log(arg) },
};
WebAssembly.instantiateStreaming(fetch("http://developer.mozilla.org/simple.wasm"), importObject).then(
(obj) => obj.instance.exports.exported_func(),
);
The ResultObject's .instance property is then accessed, and the contained exported function invoked.
Specifications
| Specification |
|---|
| WebAssembly JavaScript Interface # webassembly-namespace |
Browser compatibility
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