如何根据<select>另一个选项选择限制选项

Question

我正在尝试根据另一个选择限制选项的数量。例如，在这个例子中，"你跳过的课程有多少学分？"应该限制为等于或小于上一个问题"你这学期总共修了多少学分？"。因此，如果我在学期只修了 9 个学分，那么我跳过多少学分的第二个问题应该等于或小于整个学期的 9 个学分。

任何帮助将不胜感激。

这是jsfiddle：http://jsfiddle.net/k7tDP/1/

这是JS：

function calculateCost() {
'use strict';
// enter annual tuition
var $annualTuition = parseInt($('#annual_tuition').val());
// tuition per semester
var semesterTuition = Math.round($annualTuition / 3);
// total number of credits for semester
var $semesterCredits = parseInt($('#semester_credits').val());
// cost of a single credit
var singleCreditCost = semesterTuition / $semesterCredits;
// total credits for class being skipped
var $skippedTotalCredits = parseInt($('#skipped_total_credits').val());
// total cost for class being skipped
var skippedTotalCreditsCost = $skippedTotalCredits * singleCreditCost;
// number of times skipped class meets per week
var $skippedWeekDays = parseInt($('#skipping_class_meet').val());
// from date
var fromDate = $('#from').datepicker('getDate');
// to date
var toDate = $('#to').datepicker('getDate');
// calculate number of weeks in date range (semester) using 'from / to' dates
var skippedWeeks = Math.ceil((toDate - fromDate) / (1000 * 7 * 60 * 60 * 24));
console.log(skippedWeeks);
// total number of days in semester for class being skipped
//var $skippedTotalDays = parseInt($('#skipped_total_days').val());
var skippedTotalDays = $skippedWeekDays * skippedWeeks;
// (total cost of class) / (total number of class days in semester) = cost of class
var skippedSingleClassCost = skippedTotalCreditsCost / skippedTotalDays;
return skippedSingleClassCost.toFixed(2);
}
$(function() {
'use strict';
$('#from').datepicker({
defaultDate: '+1w',
changeMonth: true,
numberOfMonths: 1,
onSelect: function() {
//toDate = $(this).datepicker('getDate');
}
});
$('#to').datepicker({
defaultDate: '+1w',
changeMonth: true,
numberOfMonths: 1,
onSelect: function() {
//fromDate = $(this).datepicker('getDate');
}
});
$('#cost').on('click', function() {
$('.costFigure').fadeIn('fast');
$('#costTotal').html(calculateCost());
});
});

这是 html：

<form id="costForm" action="#" onsubmit="#">
<div>
<label for="annual_tuition">What is your annual tuition (estimated)?</label>
<div class="styled_select">
<select name="annual_tuition" id="annual_tuition" value="tuition amount" autofocus>
<option value="0">&nbsp;</option>
<option value="5000">$5,000</option>
<option value="10000">$10,000</option>
<option value="15000">$15,000</option>
<option value="20000">$20,000</option>
<option value="25000">$25,000</option>
<option value="30000">$30,000</option>
<option value="35000">$35,000</option>
<option value="40000">$40,000</option>
<option value="45000">$45,000</option>
<option value="50000">$50,000</option>
</select>
</div>
</div>
<div>
<label for="semester_credits">How many total credits are you taking this semester?</label>
<div class="styled_select">
<select name="semester_credits" id="semester_credits" value="" tabindex="2">
<option value="0">&nbsp;</option>
<option value="3">3 credits</option>
<option value="6">6 credits</option>
<option value="9">9 credits</option>
<option value="12">12 credits</option>
<option value="13">13 credits</option>
<option value="14">14 credits</option>
<option value="15">15 credits</option>
<option value="16">16 credits</option>
<option value="17">17 credits</option>
<option value="18">18 credits</option>
</select>
</div>
</div>
<div>
<label for="skipped_total_credits">How many credits is the class you skipped?</label>
<div class="styled_select">
<select name="skipped_total_credits" id="skipped_total_credits" value="" tabindex="2">
<option value="0">&nbsp;</option>
<option value="3">3 credits</option>
<option value="6">6 credits</option>
<option value="9">9 credits</option>
<option value="12">12 credits</option>
<option value="13">13 credits</option>
<option value="14">14 credits</option>
<option value="15">15 credits</option>
<option value="16">16 credits</option>
<option value="17">17 credits</option>
<option value="18" disabled>18 credits</option>
</select>
</div>
</div>
<div>
<label for="skipping_class_meet">How many times a week does the class you skipped meet?</label>
<div class="styled_select">
<select name="skipping_class_meet" id="skipping_class_meet" value="" tabindex="2">
<option value="0">&nbsp;</option>
<option value="1">1 time a week</option>
<option value="2">2 times a week</option>
<option value="3">3 times a week</option>
<option value="4">4 times a week</option>
<option value="5">5 times a week</option>
</select>
</div>
</div>

<div class="dateRange clearfix">
<label>Between what months are you enrolled in this class?</label>
<div style="width: 48%; float: left;">
<label for="from">From:</label>
<input type="text" id="from" name="from">
</div>
<div style="width: 48%; float: right;">
<label for="to">To:</label>
<input type="text" id="to" name="to">
</div>
</div>
<div>
<button id="cost" type="button">Calculate</button>
</div>
<div class="costFigure">
<h1>your missed class cost you $<span id="costTotal"></span></h1>
</div>
</form>

Answer 1

在changedropdown触发onchange，并根据值进行第二次dropdownenable或disabled。

$("#semester_credits").change(function () {
var $this=this;
$("#skipped_total_credits").children().each(function(){
$(this).attr("disabled",parseInt($this.value) < parseInt(this.value));
});
});

在这里检查小提琴

编辑

$this.value 包含从下拉列表中选择的值"semester_credits"现在对于"skipped_total_credits"的每个子值，我正在检查该值是否小于子值，然后将其禁用，即attr("disabled", true)否则使该子项启用。

Answer 2

我创建了一个快速函数来帮助您，可能有一种更简洁的方法可以做到这一点，但它做得很好！

元素的更改#semester_credits我获取值(学期学分数，然后循环下一个选择框并删除具有比所选值更高的选项)，我使用全局var来缓存已删除的选项，以防用户改变主意并且我们需要将它们重新添加。

$(function () {
var savedOpts = "";
$('#semester_credits').change(function() {
//Add all options back in;
if( savedOpts ) {
$('#skipped_total_credits').append(savedOpts);
savedOpts = "";
}
//Return false if blank option chosen;
if( $(this).val() === "0" )
return false;
var chosenCreds = parseInt($(this).val());
$('#skipped_total_credits option').each(function() {
var thisCred = parseInt($(this).val());
if(thisCred > chosenCreds) { 
//Remove
savedOpts += $(this)[0].outerHTML;
$(this).remove();
}
});
});

这里有一个更新的小提琴

p.s Kai Hartmann 建议的例子也是实现这一目标的好方法。

Answer 3

如果您希望根据以前的答案更改问题的下拉列表，则需要向每个select元素添加一个onchange事件，该事件将更新另一个下拉列表。然后，这应该调用一个函数，该函数删除或添加表单中的元素。

否则，您可以为Calculate按钮添加验证函数。