WebAssembly.Global
A WebAssembly.Global
object 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.
Constructor
WebAssembly.Global()
-
Creates a new
Global
object.
Global instances
All Global
instances inherit from the Global()
constructor's prototype object — this can be modified to affect all Global
instances.
Instance properties
Global.prototype.constructor
-
Returns the function that created this object's instance. By default this is the
WebAssembly.Global()
constructor. Global.prototype[@@toStringTag]
-
The initial value of the @@toStringTag property is the String value "WebAssembly.Global".
Global.prototype.value
-
The 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 the WebAssembly.Global()
constructor. It is being defined as a mutable i32
type, with a value of 0.
The value of the global is then changed, first to 42
using the Global.value
property, and then to 43 using the incGlobal()
function exported out of the global.wasm
module (this adds 1 to whatever value is given to it and then returns the new value).
js
const output = document.getElementById("output");
function assertEq(msg, got, expected) {
const result =
got === expected
? `SUCCESS! Got: ${got}<br>`
: `FAIL!<br>Got: ${got}<br>Expected: ${expected}<br>`;
output.innerHTML += `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 example running live on GitHub; see also the source code.
Specifications
Specification |
---|
WebAssembly JavaScript Interface # globals |
Browser compatibility
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