在javascript中获取下拉框的价值

Question

我正在尝试获取下拉框的值并继续获取错误Uncaught TypeError：无法读取属性'selectedIndex'为null。

继承我的代码：

JS

expirationYearSelectedIndex = document.getElementById("selYear").selectedIndex;
    console.log("expirationYearSelectedIndex = " + expirationYearSelectedIndex);

    expirationYear = document.getElementById("selYear").options[expirationYearSelectedIndex].value;
    console.log("expirationYear = " + expirationYear);

HTML

<form action="">
    <select id="SelYear" name="selYear">
        <option selected value=""> Select a Major....</option>
        <option value="Comptuer Information Systems"> CIS</option>
        <option value="Math"> M</option>
        <option value="CS"> CS</option>
        <option value="History"> H</option>
    </select>
</form>

Answer 1

错过了ID <select id="SelYear" name="selYear">

上的大写字母S.

document.getElementById("SelYear");