使用 Javascript onkeyup(） 更改 IE8 中的不透明度(再次）

我提前为发布另一个IE不透明度问题道歉，但是我已经阅读了至少30个不同的页面（许多在SO上），并且无法使其工作。

我正在尝试根据用户在卡号<input>字段中键入的第一个字符动态更改美国 4 种主要信用卡类型（Visa、MC、Amex、Discover）的不透明度。

我的代码在IE9，Firefox，Safari和Chrome中运行良好，但当然不是IE8，这是Windows XP支持所必需的。

我尝试使用以下方法进行设置：

object.style.filter = 'alpha(opacity=13)';
object.filter = 'alpha(opacity=13)';
object.style.filter = 'progid:DXImageTransform.Microsoft.Alpha(Opacity=13)';

我什至尝试在不透明度中大写 O，没想到它会有所帮助......

有谁知道我错过了什么？

JQuery 解决方案很好，但我想知道出于学术原因在 Javascript 中是否可行......

我有以下 HTML：

<span>
  <input name='cardnumber' value="3717XXXXXXX8775" type='text' id='cardnumber' onkeyup='setCardType();'>
</span>
<span>
  <img src='/style/icon_visa.gif' id='visa' alt='This is a Visa' style='opacity:.13;filter:alpha(opacity=13);'>&nbsp;&nbsp;
  <img src='/style/icon_mastercard.gif' id='mastercard' alt='This is a MasterCard' style='opacity:.13;filter:alpha(opacity=13);'>&nbsp;&nbsp;
  <img src='/style/icon_amex.gif' id='amex' alt='This is an American Express' style='opacity:1;filter:alpha(opacity=100);'>&nbsp;&nbsp;
  <img src='/style/icon_discover.gif' id='discover' alt='This is a Discover Card' style='opacity:.13;filter:alpha(opacity=13);'>
</span>
<input type='hidden' name='cardtype' id='cardtype' value="American Express">

和以下Javascript：

function setCardType() {
var cardnumber = document.getElementById('cardnumber').value;
cardnumber = cardnumber.replace(/[^0-9]/g,'');
document.getElementById('cardnumber').value = cardnumber;
var firstchar = document.getElementById('cardnumber').value.charAt(0);
if (firstchar == 3) {
    if (document.getElementById('visa').style.opacity) {
        document.getElementById('visa').style.opacity = .13;
        document.getElementById('mastercard').style.opacity = .13;
        document.getElementById('amex').style.opacity = 1;
        document.getElementById('discover').style.opacity = .13;
    }
    else {
        document.getElementById('visa').style.filter = 'alpha(opacity=13)';
        document.getElementById('mastercard').style.filter = 'alpha(opacity=13)';
        document.getElementById('amex').style.filter = 'alpha(opacity=100)';
        document.getElementById('discover').style.filter = 'alpha(opacity=13)';
    }
    document.getElementById('confirmCardType').innerHTML = 'American Express';
}
else if (firstchar == 4) {
    if (document.getElementById('visa').style.opacity) {
        document.getElementById('visa').style.opacity = 1;
        document.getElementById('mastercard').style.opacity = .13;
        document.getElementById('amex').style.opacity = .13;
        document.getElementById('discover').style.opacity = .13;
    }
    else {
        document.getElementById('visa').style.filter = 'alpha(opacity=100)';
        document.getElementById('mastercard').style.filter = 'alpha(opacity=13)';
        document.getElementById('amex').style.filter = 'alpha(opacity=13)';
        document.getElementById('discover').style.filter = 'alpha(opacity=13)';
    }
    document.getElementById('confirmCardType').innerHTML = 'Visa';
}
else if (firstchar == 5) {
    if (document.getElementById('visa').style.opacity) {
        document.getElementById('visa').style.opacity = .13;
        document.getElementById('mastercard').style.opacity = 1;
        document.getElementById('amex').style.opacity = .13;
        document.getElementById('discover').style.opacity = .13;
    }
    else {
        document.getElementById('visa').style.filter = 'alpha(opacity=13)';
        document.getElementById('mastercard').style.filter = 'alpha(opacity=100)';
        document.getElementById('amex').style.filter = 'alpha(opacity=13)';
        document.getElementById('discover').style.filter = 'alpha(opacity=13)';
    }
    document.getElementById('confirmCardType').innerHTML = 'MasterCard';
}
else if (firstchar == 6) {
    if (document.getElementById('visa').style.opacity) {
        document.getElementById('visa').style.opacity = .13;
        document.getElementById('mastercard').style.opacity = .13;
        document.getElementById('amex').style.opacity = .13;
        document.getElementById('discover').style.opacity = 1;
    }
    else {
        document.getElementById('visa').style.filter = 'alpha(opacity=13)';
        document.getElementById('mastercard').style.filter = 'alpha(opacity=13)';
        document.getElementById('amex').style.filter = 'alpha(opacity=13)';
        document.getElementById('discover').style.filter = 'alpha(opacity=100)';
    }
    document.getElementById('confirmCardType').innerHTML = 'Discover';
}
else {
    if (document.getElementById('visa').style.opacity) {
        document.getElementById('visa').style.opacity = .13;
        document.getElementById('mastercard').style.opacity = .13;
        document.getElementById('amex').style.opacity = .13;
        document.getElementById('discover').style.opacity = .13;
    }
    else {
        document.getElementById('visa').style.filter = 'alpha(opacity=13)';
        document.getElementById('mastercard').style.filter = 'alpha(opacity=13)';
        document.getElementById('amex').style.filter = 'alpha(opacity=13)';
        document.getElementById('discover').style.filter = 'alpha(opacity=13)';
    }
    document.getElementById('confirmCardType').innerHTML = '';
}
return true;

}

编辑：这是jQuery解决方案，它大大缩短了代码：

function setCardType() {
var cardnumber = document.getElementById('cardnumber').value;
cardnumber = cardnumber.replace(/[^0-9]/g,'');
document.getElementById('cardnumber').value = cardnumber;
var firstchar = cardnumber.charAt(0);
if (firstchar == 3) {
    $('#visa').css('opacity', .13);
    $('#mastercard').css('opacity', .13);
    $('#amex').css('opacity', 1);
    $('#discover').css('opacity', .13);
    document.getElementById('confirmCardType').innerHTML = 'American Express';
}
else if (firstchar == 4) {
    $('#visa').css('opacity', 1);
    $('#mastercard').css('opacity', .13);
    $('#amex').css('opacity', .13);
    $('#discover').css('opacity', .13);
    document.getElementById('confirmCardType').innerHTML = 'Visa';
}
else if (firstchar == 5) {
    $('#visa').css('opacity', .13);
    $('#mastercard').css('opacity', 1);
    $('#amex').css('opacity', .13);
    $('#discover').css('opacity', .13);
    document.getElementById('confirmCardType').innerHTML = 'MasterCard';
}
else if (firstchar == 6) {
    $('#visa').css('opacity', .13);
    $('#mastercard').css('opacity', .13);
    $('#amex').css('opacity', .13);
    $('#discover').css('opacity', 1);
    document.getElementById('confirmCardType').innerHTML = 'Discover';
}
else {
    $('#visa').css('opacity', .13);
    $('#mastercard').css('opacity', .13);
    $('#amex').css('opacity', .13);
    $('#discover').css('opacity', .13);
    document.getElementById('confirmCardType').innerHTML = '';
}
return true;

}