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WebAssembly.Module() constructor
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.
A WebAssembly.Module() constructor creates a new Module
object containing stateless WebAssembly code that has already been compiled by the
browser and can be efficiently shared with Workers, and instantiated multiple times.
The WebAssembly.Module() constructor function can be called to
synchronously compile given WebAssembly binary code. However, the primary way to get a
Module is through an asynchronous compilation function like
WebAssembly.compile().
Warning:
Since compilation for large modules can be expensive,
developers should only use the Module() constructor when synchronous
compilation is absolutely required; the asynchronous
WebAssembly.compileStreaming() method should be used at all other times.
Note:
Webpages that have strict Content Security Policy (CSP) might block WebAssembly from compiling and executing modules.
For more information on allowing WebAssembly compilation and execution, see the script-src CSP.
js
new WebAssembly.Module(bufferSource)
new WebAssembly.Module(bufferSource, compileOptions)
- If the parameter is not of the correct type or structure, a
TypeError is thrown.
- If compilation fails, the constructor rejects with a
WebAssembly.CompileError.
- Some browsers may throw a
RangeError, as they prohibit compilation and instantiation of Wasm with large buffers on the UI thread.
js
const importObject = {
my_namespace: {
imported_func(arg) {
console.log(arg);
},
},
};
function createWasmModule(bytes) {
return new WebAssembly.Module(bytes);
}
fetch("simple.wasm")
.then((response) => response.arrayBuffer())
.then((bytes) => {
const mod = createWasmModule(bytes);
WebAssembly.instantiate(mod, importObject).then((result) =>
result.exports.exported_func(),
);
});
This example enables JavaScript string builtins and imported global string constants when compiling a Wasm module via the Module() constructor, which is then instantiated with instantiate(). It then calls the exported main() function, which logs "hello world!" to the console. See it running live.
js
const importObject = {
// Regular import
m: {
log: console.log,
},
};
const compileOptions = {
builtins: ["js-string"], // Enable JavaScript string builtins
importedStringConstants: "string_constants", // Enable imported global string constants
};
fetch("log-concat.wasm")
.then((response) => response.arrayBuffer())
.then((bytes) => {
const module = new WebAssembly.Module(bytes, compileOptions);
WebAssembly.instantiate(module, importObject).then((instance) =>
instance.exports.main(),
);
});