The following spec tests jsapi.js fail: test(() => { const compileDesc = Object.getOwnPropertyDescriptor(WebAssembly, 'compile'); assert_equals(typeof compileDesc.value, "function"); assert_equals(compileDesc.writable, true); assert_equals(compileDesc.enumerable, false); assert_equals(compileDesc.configurable, true); }, "'WebAssembly.compile' data property"); test(() => { const compile = WebAssembly.compile; const compileDesc = Object.getOwnPropertyDescriptor(WebAssembly, 'compile'); assert_equals(compile, compileDesc.value); assert_equals(compile.length, 1); assert_equals(compile.name, "compile"); }, "'WebAssembly.compile' function"); I'll leave a FIXME for now.