I'm trying to make a JavaScript function to validate the month and year from a field. The format of the date on the field is mm/yyyy and the function that validates it's the one below:

function validateVencimento(){
    var valid = true;
    var currentTime = new Date();
    var actualMonth = currentTime.getMonth() + 1;
    var actualYear = currentTime.getFullYear();
    vencimento = vencimento.replace('///g', '');

    var month = parseInt(vencimento.substring(0, 2),10);
    var year  = parseInt(vencimento.substring(2, 6),10);

    if((month < 1) || (month > 12)) valid = false;
    if((year < actualYear)) valid = false;
    if((year < actualYear) && (month < actualMonth)) valid = false;

    if(valid == false){
        vencimento.addClass("error");
        vencimentoInfo.text("A validade do cartao esta invalida!");
        vencimentoInfo.addClass("error");
        return false;
    }

    else{
        vencimento.removeClass("error");
        vencimentoInfo.text("");
        vencimentoInfo.removeClass("error");
        return true;
    }
}

After i enter the date on the field i call the function above on blur, but the Chrome console returns the error Uncaught TypeError: Object # has no method 'replace'.