Javascript 选择并选择默认值以外的选项_Javascript

Javascript 选择并选择默认值以外的选项

javascript

Javascript 选择并选择默认值以外的选项,javascript,Javascript,在用户单击submit按钮从选择框中选择一个选项（而不是使用javascript的默认值）之后，我该如何提醒用户这是我的代码 <select id = "Sel"> <option value ="Song1">default value<br> <option value ="Song2">Break on through<br> <option value ="Song3">Time<br&

在用户单击submit按钮从选择框中选择一个选项（而不是使用javascript的默认值）之后，我该如何提醒用户这是我的代码

<select id = "Sel">
    <option value ="Song1">default value<br>
    <option value ="Song2">Break on through<br>
    <option value ="Song3">Time<br>
    <option value ="Song4">Money<br>
    <option value="Song5">Saucerful of Secrets
</select><br><br>

谢谢

首先，您的标记是错误的。。需要关闭“开始选项”标记

在更改事件中检查值。。。如果值为Song1，则向用户发出警报

HTML

试试这个：

<html>
    <head>
        <script src="//ajax.googleapis.com/ajax/libs/jquery/1.8.3/jquery.min.js"></script>
        <script type="text/javascript">
            $(document).ready(function() {
                $('#Sel').change(function() {
                    if($(this).val()=="Song1"){
                        alert('bad');
                    }else{
                        alert('good');
                    }
                });
                $('#button-test').click(function() {
                    var bob = $('#Sel').val();
                    if (bob=='Song1'){
                        alert('bad');
                    }else{
                        alert('good');
                    }
                });
            });
        </script>
    </head>
<body>

<select id = "Sel">
    <option value ="Song1">default value</option>
    <option value ="Song2">Break on through</option>
    <option value ="Song3">Time</option>
    <option value ="Song4">Money</option>
    <option value="Song5">Saucerful of Secrets</option>
</select><br>
<br>
<button id="button-test">

首先，你的标记是不正确的。。更正为

<select id = "Sel">
    <option value ="Song1">default value</option>
    <option value ="Song2">Break on through</option>
    <option value ="Song3">Time</option>
    <option value ="Song4">Money</option>
    <option value="Song5">Saucerful of Secrets</option>
</select><br><br>

或

到目前为止，您的javascript是什么样子的？您的标记不正确。标记未关闭。让我们看看你做了什么，你有什么问题。@johnynguyen。。很高兴它能起作用：

var elem = document.getElementById('submit');

elem.addEventListener('click', function(){
   var selectElem = document.getElementById('Sel');
   var val = selectElem.value;
    if(val == 'Song1'){
        alert('Select an option!!');
        return false;
    }        
});

<html>
    <head>
        <script src="//ajax.googleapis.com/ajax/libs/jquery/1.8.3/jquery.min.js"></script>
        <script type="text/javascript">
            $(document).ready(function() {
                $('#Sel').change(function() {
                    if($(this).val()=="Song1"){
                        alert('bad');
                    }else{
                        alert('good');
                    }
                });
                $('#button-test').click(function() {
                    var bob = $('#Sel').val();
                    if (bob=='Song1'){
                        alert('bad');
                    }else{
                        alert('good');
                    }
                });
            });
        </script>
    </head>
<body>

<select id = "Sel">
    <option value ="Song1">default value</option>
    <option value ="Song2">Break on through</option>
    <option value ="Song3">Time</option>
    <option value ="Song4">Money</option>
    <option value="Song5">Saucerful of Secrets</option>
</select><br>
<br>
<button id="button-test">

<select id = "Sel">
    <option value ="Song1">default value</option>
    <option value ="Song2">Break on through</option>
    <option value ="Song3">Time</option>
    <option value ="Song4">Money</option>
    <option value="Song5">Saucerful of Secrets</option>
</select><br><br>

if(document.getElementById('Sel').value=="Song1")
    return false;

if(document.getElementById('Sel').selectedIndex ==0)
    return false;

<script>
     $(document).ready(function() {
        $("#Sel").live('click', function (event) {
        var myval=$(this).val;
        alert(myval);
        });
    </script>   
    <select id = "Sel">
            <option name="opSel" value ="Song1">default value</option>
            <option name="opSel" value ="Song2">Break on through</option>
            <option name="opSel" value ="Song3">Time</option>
            <option name="opSel" value ="Song4">Money</option>
            <option name="opSel" value="Song5">Saucerful of Secrets</option>
        </select>