使用jQuery使用SELECT字段进行表单验证

Question

Jquery Isn't alerting me when their is no value selected from the Rating form. Would it be because selected="selected" is actually being seen as a value to jquery ?

  <label for="rating">Rating</label>
    <select id="rating" name="rating" />
        <option selected="selected" disabled="disabled">Select a Rating</option>
        <option value="Terrible">Terrible</option>
        <option value="Fair">Fair</option>
        <option value="Ok">Ok</option>
        <option value="Good">Good</option>
        <option value="Excellent">Excellent</option>
       </select>


      $(document).ready(function(){

        // No value for movie_title
        if ($('#movie_title').val() == "" ) {
            alert ("No Film");
        }

        // No Value for actor
        if ($('#leading_name').val() == "") {
            alert ("No actor");
        }

        // No value for rating
        if ($('#rating').val() == "") {
            alert ("No Rating");
        }

        //No value for review
        if ($('#review').val() == "") {
            alert ("No review");
        }

    // Focus on first form field.
        $("input:text:visible:first").focus();

   })

Answer 1

That's because the default value will be the text if no value is specified.

Give a value of 0 to your default option and check against that:

<option selected="selected" value=0 disabled="disabled">Select a Rating</option>

Answer 2

$('#rating').val() returns null :

http://jsfiddle.net/KFpFq/

Adding a value attribute doesn't appear to work in Chrome, though checking for null does.

console.log($('#rating').val()); //null
console.log($('#rating').val() == "0"); //false
console.log($('#rating').val() == null); //true

Answer 3

您可以使用本机selectedIndex查找第一个选择的索引-https: //developer.mozilla.org/en-US/docs/Web/API/HTMLSelectElement

if($('#rating').get(0).selectedIndex === 0){alert("first item")}