使用JavaScript级联下拉列表不起作用

Question

我在javascript中有此代码，但无法正常工作。 有人可以检查我的代码吗？ 顺便说一下，我只是从这里的一个问题中得到了这段代码。 谢谢

function CollegeDepartment() {
    var s1 = document.getElementById("college");
    var s2 = document.getElementById("department");
    s2.innerHTML = "";
    if (s1.value == "College of Engineering") {
        var optionArray = ["Civil Engineering", "Computer Engineering", "Electrical Engineering", "Electronics and Communication Engineering, Industrial Engineering, Mechanical Engineering"];
    } else if (s1.value == "CAS") {
        var optionArray = ["Political Science", "Mascomm", "Liacomm"];
    } else if (s1.value == "Commerce") {
        var optionArray = ["Business Ad", "Hotel Management", "Tourism"];
    } else if (s1.value == "Education") {
        var optionArray = ["SPED"];
    } else if (s1.value == "CICCT") {
        var optionArray = ["Computer Science", "Information Technology"];
    }

    for (var option in optionArray) {
        var newOption = document.createElement("option");
        newOption.value = optionArray[option];
        newOption.innerHTML = optionArray[option];
        s2.options.add(newOption);
    }
};

编辑：

的HTML

 <select class="form-control" name="college" id="college" runat="server" oninput="CollegeDepartment()">
                 <option selected>Select College</option>
                 <option value="College of Engineering">College of Engineering</option>
                 <option value="CAS">College of Arts and Science</option>
                 <option value="Commerce">College of Commerce</option>
                 <option value="Education">College of Education</option>
                 <option value="CICCT">CICCT</option>   
             </select>
        </div>
            <br />

        <div class="form-group">
            <select id="department" name="department" class="form-control" runat="server" placeholder="Department" >
                <option value="Department" selected>Select Department</option>
            </select>
        </div>

Answer 1

立即发现您的问题，您正在使用oninput事件，您需要的是onchange

所以这：

 <select class="form-control" name="college" id="college" runat="server" oninput="CollegeDepartment()">

成为：

 <select class="form-control" name="college" id="college" runat="server" onchange="CollegeDepartment()">

 function CollegeDepartment() { var s1 = document.getElementById("college"); var s2 = document.getElementById("department"); s2.innerHTML = ""; if (s1.value == "College of Engineering") { var optionArray = ["Civil Engineering", "Computer Engineering", "Electrical Engineering", "Electronics and Communication Engineering, Industrial Engineering, Mechanical Engineering"]; } else if (s1.value == "CAS") { var optionArray = ["Political Science", "Mascomm", "Liacomm"]; } else if (s1.value == "Commerce") { var optionArray = ["Business Ad", "Hotel Management", "Tourism"]; } else if (s1.value == "Education") { var optionArray = ["SPED"]; } else if (s1.value == "CICCT") { var optionArray = ["Computer Science", "Information Technology"]; } for (var option in optionArray) { var newOption = document.createElement("option"); newOption.value = optionArray[option]; newOption.innerHTML = optionArray[option]; s2.options.add(newOption); } }; 

 <select class="form-control" name="college" id="college" runat="server" onchange="CollegeDepartment()"> <option selected>Select College</option> <option value="College of Engineering">College of Engineering</option> <option value="CAS">College of Arts and Science</option> <option value="Commerce">College of Commerce</option> <option value="Education">College of Education</option> <option value="CICCT">CICCT</option> </select> </div> <br /> <div class="form-group"> <select id="department" name="department" class="form-control" runat="server" placeholder="Department" > <option value="Department" selected>Select Department</option> </select> </div> 

试试上面的片段，或者这里是一个CodePen： http ://codepen.io/anon/pen/PPpWJp