It's defined by TypeScript itself in typescript/lib/lib.dom.d.ts:

declare namespace WebAssembly {
    interface Module {
    }

    var Module: {
        prototype: Module;
        new(bytes: BufferSource): Module;
        customSections(moduleObject: Module, sectionName: string): ArrayBuffer[];
        exports(moduleObject: Module): ModuleExportDescriptor[];
        imports(moduleObject: Module): ModuleImportDescriptor[];
    };

    ...
}

Maybe you're using an old version of TypeScript?

Hey @evanw
I use typescript 4.7.3. I see that the WebAssembly namespace is there in node_modules\typescript\lib\lib.dom.d.ts indeed, but TypeScript doesn't pick that up. 🤔

Here is the project that the problem exists if you'd like to check yourself: https://github.com/doteric/funpack

This is because you have "lib": ["es2021"], while WebAssembly is in "dom".

The simplest solution would be changing your tsconfig to "lib": ["es2021", "dom"], however it may be wrong because your code are not supposed to be run in the browser.

Another solution I was thinking about is installing @types/node since there's also a WebAssembly in node environment, however I looked into that package and unfortunately I didn't find the definition. Some references: DefinitelyTyped/DefinitelyTyped#48648 DefinitelyTyped/DefinitelyTyped#57055 It looks like they are facing the problem of global type conflicting with the built-in ones.

Another choice would be esbuild trying to loose the type constraints, providing a minimal WebAssembly.Module that mimics the one in the "dom", for example:

interface WebAssemblyModule {}
...
wasmModule?: WebAssemblyModule

Thanks for looking into this @hyrious
Pretty interesting, and yeah dom wouldn't really fit into the package as it's only used on node.
For now I'm fine with going with skipLibCheck, but just reported this issue for the awareness 😄

Ok. I'm going to close this since the dom library is how TypeScript has chosen to ship type annotations for the WebAssembly API. This is a problem with TypeScript, not with esbuild. See also microsoft/TypeScript#47381 and microsoft/TypeScript-DOM-lib-generator#826.