WebAssembly.Global
Baseline Widely available
This feature is well established and works across many devices and browser versions. It’s been available across browsers since March 2020.
AWebAssembly.Global object represents a global variable instance, accessible from both JavaScript and importable/exportable across one or moreWebAssembly.Module instances. This allows dynamic linking of multiple modules.
Constructor
WebAssembly.Global()Creates a new
Globalobject.
Global instances
AllGlobal instances inherit from theGlobal() constructor's prototype object — this can be modified to affect allGlobal instances.
Instance properties
Global.prototype.constructorReturns the function that created this object's instance. By default this is the
WebAssembly.Global()constructor.Global.prototype[Symbol.toStringTag]The initial value of the
[Symbol.toStringTag]property is the String value "WebAssembly.Global".Global.prototype.valueThe value contained inside the global variable — this can be used to directly set and get the global's value.
Instance methods
Global.prototype.valueOf()Old-style method that returns the value contained inside the global variable.
Examples
Creating a new Global instance
The following example shows a new global instance being created using theWebAssembly.Global() constructor. It is being defined as a mutablei32 type, with a value of 0.
The value of the global is then changed, first to42 using theGlobal.value property, and then to 43 using theincGlobal() function exported out of theglobal.wasm module (this adds 1 to whatever value is given to it and then returns the new value).
const output = document.getElementById("output");function assertEq(msg, got, expected) { const result = got === expected ? `SUCCESS! Got: ${got}\n` : `FAIL!\nGot: ${got}\nExpected: ${expected}\n`; output.innerText += `Testing ${msg}: ${result}`;}assertEq("WebAssembly.Global exists", typeof WebAssembly.Global, "function");const global = new WebAssembly.Global({ value: "i32", mutable: true }, 0);WebAssembly.instantiateStreaming(fetch("global.wasm"), { js: { global } }).then( ({ instance }) => { assertEq( "getting initial value from wasm", instance.exports.getGlobal(), 0, ); global.value = 42; assertEq( "getting JS-updated value from wasm", instance.exports.getGlobal(), 42, ); instance.exports.incGlobal(); assertEq("getting wasm-updated value from JS", global.value, 43); },);Note:You can see the examplerunning live on GitHub; see also thesource code.
Specifications
| Specification |
|---|
| WebAssembly JavaScript Interface # globals |