使用html表单验证的Javascript无效

Question

我正在尝试使用简单的javascript脚本验证表单,但它不起作用,有人能告诉我我的代码有什么问题吗？(对不起我的模糊问题)

JS代码:

<script type="text/javascript">
function validation()
{                                 
    var fName=document.forms["teacherReg"]["firstname"].value;
    var lName=document.forms["teacherReg"]["lastname"].value;
    var uName=document.forms["teacherReg"]["username"].value;
    var pWord=document.forms["teacherReg"]["password"].value;
    var cPWord=document.forms["teacherReg"]["confirmpassword"].value;

    if (fName="" || lName="" || uName="" || pWord="")
    {
        alert("Not a valid entry");
        return false;
    }

}
</script>

HTML格式:

<form name="teacherReg" action="" method="POST" onsubmit="return validation();">
    1. First name:
    &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
    2. Last name:<br/><input type="text" name="firstname" id="firstname" />
    &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
    <input type="text" name="lastname" id="lastname" /><br/><br/>                             
    3. Desired Username:
    <br/><input type="text" name="username" id="username" /><br/><br/>
    4. Desired Password:
    &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
    5. Confirm Password:<br/><input type="password" name="password" id="password" />
    &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
    <input type="password" name="confirmpassword" id="confirmpassword" /> <br/><br/>
    <center><input type="submit" value="Register" name="submitbutton" class="button" /></center>
</form>

如果任何字段"fName,lName,uName,pWord"为空,我希望它返回false,但它总是返回true

Answer 1

问题是您将=(赋值运算符)运算符与==(比较运算符)混淆:

if (fName = "" || lName = "" || uName = "" || pWord = "") {

它应该是

if (fName == "" || lName == "" || uName == "" || pWord == "") {

修正演示:http://jsfiddle.net/49xDH/