如何使用JavaScript禁用表单下拉选项

Question

我试图在页面加载后在下拉列表中选择“选择”时禁用表单中的“名称”文本字段（在页面加载时被禁用），即在我选择了其他两个选项之一之后禁用或启用该字段，当我返回“选择”时，我希望禁用同一字段。 我不明白为什么我编写的JavaScript可以防止这种情况的发生。 谢谢！

        <script type="text/javascript">

    function clickclear(thisfield, defaulttext) {
        if (thisfield.value === defaulttext) {
            thisfield.value = "";
        }
    }

    function clickrecall(thisfield, defaulttext) {
        if (thisfield.value === "") {
            thisfield.value = defaulttext;
        }
    }

    function checkPickup() {

        if (form.os0.value != "Pickup from Toowong, Brisbane" ) {
            form.name.disabled = false; form.name.style.color = '#333';

        } else {

            form.name.disabled = true; form.name.style.color = '#CCC';
            /* Reset form values */
            form.name.value = "His/her name";
        }
    }
</script>

<script type="text/javascript">
    function validate(form) {

        var errmsg = "Oops, you're required to complete the following fields! \n";

        // Various other form validations here

        // Validate "Pickup"
        if (form.os0.value === "") {
            errmsg = errmsg + " - Choose pickup or delivery\n";
        }

        // Validate "phone"
        if (form.phone.value === "" || form.phone.value === "Mobile's best!") {
            errmsg = errmsg + " - Your phone number\n";
        }


        if (form.os0.value != "Pickup from Toowong, Brisbane") {

            // Validate "name"
            if (form.name.value === "" || form.name.value === "His/her name") {
                errmsg = errmsg + " - His/her name\n";
            }
        }

        // Alert if fields are empty and cancel form submit
        if (errmsg === "Oops, you're required to complete the following fields! \n") {
            form.submit();
        } else {
            alert(errmsg);
            return false;
        }
    }
</script>
    </head>
    <body>
        <form name="form" action="https://www.paypal.com/cgi-bin/webscr" method="post" onSubmit="return validate(form)">

            <p class="row">
                <input type="hidden" name="on0" value="Pickup and delivery" />Pickup and delivery<br />
                <select name="os0" onchange="checkPickup()">
                    <option value="" selected >Choose</option>
                    <option value="Pickup from Toowong, Brisbane">Pickup from Toowong, Brisbane $1.00 AUD</option>
                    <option value="Brisbane +$23.60">Brisbane +$23.60 =$1.00 AUD</option>
                </select>
            </p>
            <p class="row">Your daytime phone number<br />
                <input type="text" name="phone" value="Mobile's best!" onclick="clickclear(this, 'Mobile\'s best!')" onblur="clickrecall(this,'Mobile\'s best!')" />
            </p>
            <p class="row">Recipient's name<br />
                <input style="color: #ccc" class="name" type="text" name="name" value="His/her name" onclick="clickclear(this, 'His/her name')" onblur="clickrecall(this,'His/her name')" disabled />
            </p>
            <input name="custom" type="hidden"  />
            <input type="hidden" name="currency_code" value="AUD" />
            <input class="button" type="image" src="https://www.paypalobjects.com/en_AU/i/btn/btn_buynowCC_LG.gif" border="0" name="submit" alt="PayPal — The safer, easier way to pay online." />
            <img alt="" border="0" src="https://www.paypalobjects.com/en_AU/i/scr/pixel.gif" width="1" height="1"> -->
        </form>
    </body>
</html>

Answer 1

这可能是对您所写内容的简单误解：

if (form.os0.value != "Pickup from Toowong, Brisbane" ) {
    form.name.disabled = false; form.name.style.color = '#333';
} else {
    form.name.disabled = true; form.name.style.color = '#CCC';
    //
}

普通英语翻译如下：

如果该值不是 "Pickup from Toowong, Brisbane" ，则启用该字段，否则禁用它。

等效于：

仅当值为"Pickup from Toowong, Brisbane"时禁用该字段。

我相信您要寻找的逻辑是：

if (form.os0.value == "Brisbane +$23.60" ) {
    form.name.disabled = false; form.name.style.color = '#333';
} else {
    form.name.disabled = true; form.name.style.color = '#CCC';
    //
}

由于涉及特定案例，使用switch语句编写代码可能更漂亮。

见演示

Answer 2

您打算在问题中输入等于（==）的double还是等于（===）的三倍？ 基于查看您的代码，在我看来，您需要一个等于（==）的双精度数而不是三进制。 我认为三重可能意味着其他。

如何使用JavaScript禁用表单下拉选项

问题描述

2 个解决方案

解决方案1
0 已采纳 2012-01-31 04:09:30

解决方案2
0 2012-01-31 04:19:12

如何使用JavaScript禁用表单下拉选项

问题描述

2 个解决方案

解决方案1 0 已采纳 2012-01-31 04:09:30

解决方案2 0 2012-01-31 04:19:12

解决方案1
0 已采纳 2012-01-31 04:09:30

解决方案2
0 2012-01-31 04:19:12