WebAssembly

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 {{jsxref("Math")}}, which is also a namespace object for mathematical constants and functions, or to {{jsxref("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.Module instances. 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 buffer property is a resizable {{jsxref("ArrayBuffer")}} that holds the raw bytes of memory accessed by a WebAssembly Instance.
• 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.Module from WebAssembly binary code, leaving instantiation as a separate step.
• WebAssembly.compileStreaming()
  • : Compiles a WebAssembly.Module directly 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 Module and its first Instance.
• WebAssembly.instantiateStreaming()
  • : Compiles and instantiates a WebAssembly module directly from a streamed underlying source, returning both a Module and its first Instance.
• 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("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

{{Specifications}}

Browser compatibility

{{Compat}}

See also

• WebAssembly overview
• WebAssembly concepts
• Using the WebAssembly JavaScript API