WebAssembly.instantiate

The instantiate() method of the WebAssembly object compiles a .wasm file loaded into the JavaScript context as a typed array (e.g. using Fetch/arrayBuffer into a Module object instance and then instantiates that module, all in one step — it returns an Instance object instance.

Syntax

WebAssembly.instantiate(bufferSource, importObject).then(function(object) {
  // do something with compiled module
});

Parameters

bufferSource

A typed array containing the byte code of the .wasm module you want to compile.

importObject Optional

An object containing definitions of functions that you want to import into the WebAssembly module instance, if any.

Return value

A promise that resolves to an object representing the compiled and instantiated module. the object contains two members:

• module: A Module object instance representing the compiled WebAssembly module.
• instance: An Instance object instance representing an instance of the compiled WebAssembly module.

Exceptions

• If either of the parameters are not of the correct type or structure, a TypeError is thrown.
• If the operation fails, the promise rejects with a WebAssembly.CompileError, WebAssembly.LinkError, or WebAssembly.RuntimeError, depending on the cause of the failure.

Examples

The following example compiles and instantiates the loaded simple.wasm byte code using the WebAssembly.instantiate() method, importing a JavaScript function into the WebAssembly Module in the process — this promise resolves to an object (obj) containing the compiled Module instance, and it's instantiated Instance instance. We then export a function from the module via Instance.exports.exported_func().

var importObject = {
  imports: {
    imported_func: function(arg) {
      console.log(arg);
    }
  }
};

fetch('simple.wasm').then(function(response) {
  response.arrayBuffer().then(function(bytes) {
    WebAssembly.instantiate(bytes, importObject).then(function(obj) {
      obj.instance.exports.exported_func();
    })
  })
});

Specifications

Specification	Status	Comment
Web Assembly JavaScript API The definition of 'instantiate()' in that specification.	Draft	Initial draft definition.

Browser compatibility

[1] Experimental support can be enabled in Chrome 51+ and Opera 38+ by going to chrome://flags and enabling the Experimental WebAssembly flag.

[2] Experimental support can be enabled in Firefox 47+ by enabling the javascript.options.wasm flag in about:config.

See also

• WebAssembly landing page.
• WebAssembly concepts
• Using the WebAssembly JavaScript API