The is() prototype method of the Exception object can be used to test if the Exception matches a given tag.

The method might be used to test that a tag is correct before passing it to Exception.prototype.getArg() to get the passed values. It can be used on tags created in JavaScript or created in WebAssembly code and exported to JavaScript.

Note: It is not enough that the tag has an identical sequence of data types — it must have the same identity (be the same tag) as was used to create the exception.





An WebAssembly.Tag that can be checked to verify the type of the exception.

Return value

A boolean true if the specified tag matches the exception, and false otherwise.


The code below shows how to use is() to verify that a tag matches an Exception.

// Create tag and use it to create an exception
const tag1 = new WebAssembly.Tag({ parameters: ["i32", "f64"] });
const exception1 = new WebAssembly.Exception(tag1, [42, 42.3]);

// Verify that "tag1" matches this exception
console.log(`Tag1: ${exception1.is(tag1)}`);

// Log output:
// Tag1: true

We can also demonstrate that this exception will not match another tag even if the tag is created with the same parameters.

// Create a new tag (with same parameters) and verify it does not match the exception
const tag2 = new WebAssembly.Tag({ parameters: ["i32", "f64"] });
console.log(`Tag2: ${exception1.is(tag2)}`);

// Log output:
// Tag2: false


WebAssembly JavaScript Interface: Exception Handling
# dom-exception-is

Browser compatibility

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See also