var oSignedData = ObjCreator("CAdESCOM.CadesSignedData");
var CADES_BES = 1;
var CADESCOM_CADES_DEFAULT = 0;
var CADESCOM_BASE64_TO_BINARY = 0x01;
oSignedData.ContentEncoding = CADESCOM_BASE64_TO_BINARY;
oSignedData.Content = "U29tZSBEYXRhLg=="; // взял из примера
sSignedData = oSignedData.SignCades(oSigner, CADESCOM_CADES_BES, true);

var oSignedData = ObjCreator("CAdESCOM.CadesSignedData");
try {
oSignedData.ContentEncoding = CADESCOM_BASE64_TO_BINARY;
oSignedData.Content = "U29tZSBEYXRhLg==";
oSignedData.VerifyCades(sSignedData, CADESCOM_CADES_BES, true);
} catch (err) {
    alert("Failed to verify signature. Error: " + GetErrorMessage(err));
}