我试图弄清楚如何使用Vanilla JS在几个下拉列表中动态选择值。我有3个具有相同值的下拉列表。他们每个人应同时选择不同的值(不允许重复)。因此,一旦用户在一个列表中更改了另一个值,另一个列表的值应相应地更新。基本上,在这种情况下,我需要交换其号码。但是我无法完成任务,因为我是JS的新手,并且是编程方面的新手。我尝试了以下内容:
// defining initial values
var startPoint = document.querySelectorAll("select");
// function to recalculate value of each list on change
function calculateNewValues() {
var changes = new Array();
// getting updated values from lists as an array
var updatedValues = document.querySelectorAll("select");
// looping through array
for (let i = 0; i < updatedValues.length; i++) {
// if in updated array value of current index isn't equal to value
// of index in initial array
if (updatedValues[i].value != startPoint[i].value) {
// creating variable changes for tracking
changes[i] = updatedValues[i].value;
}
// if var changes has been defined (i.e. value of any list was updated)
if (changes.length > 0) {
// finding index of initial array with same value
var key = startPoint.findIndex(changes[i]);
// setting value of found index to previously stored value in updated list
updatedValues[key].value = startPoint[i].value;
}
}
updatedValues.forEach(element => {
console.log(element.value);
});
}
// event listeners for change of every dropdown list
const lists = document.querySelectorAll("select");
for (k = 0; k < lists.length; k++) {
lists[k].addEventListener("change", calculateNewValues, false);
}
<p>
<select name="list1" id="list1">
<option value="1" id="list1option1" selected>1</option>
<option value="2" id="list1option2">2</option>
<option value="3" id="list1option3">3</option>
</select>
</p>
<p>
<select name="list2" id="list2">
<option value="1" id="list2option1">1</option>
<option value="2" id="list2option2" selected>2</option>
<option value="3" id="list2option3">3</option>
</select>
</p>
<p>
<select name="list3" id="list3">
<option value="1" id="list3option1">1</option>
<option value="2" id="list3option2">2</option>
<option value="3" id="list3option3" selected>3</option>
</select>
</p>
我可能会在if (changes.length > 0) {
上犯一些错误但我不明白如何使这部分变得更好。
非常感谢。
您已将startPoint
分配给querySelectorAll。每当您编写相同的querySelectorAll时,它将保存完全相同的对象。因此,在您的情况下,startPoint
和updatedValues
将始终相同。
startPoint
定义为值的数组,并在setStartingPointValues()
中设置其值。target
添加为要更新的当前列表。if (target.id == updatedValues[i].id && updatedValues[i].value != startPoint[i])
并检索了target
的旧值。var key = startPoint.findIndex(x => x == target.value);
将找到具有与新值相似的值的选择。如果找到键!= -1,请使用oldValue更新该选择。setStartingPointValues()
。// defining initial values
var startPoint = [];
// store values for all select.
function setStartingPointValues() {
startPoint = [];
document.querySelectorAll("select").forEach(x => startPoint.push(x.value));
}
setStartingPointValues();
// function to recalculate value of each list on change
function calculateNewValues() {
let target = this;
let oldValue = 0;
// getting updated values from lists as an array
var updatedValues = document.querySelectorAll("select");
// looping through array
for (let i = 0; i < updatedValues.length; i++) {
// if in updated array value of current index isn't equal to value
// of index in initial array
if (target.id == updatedValues[i].id && updatedValues[i].value != startPoint[i]) {
// creating variable changes for tracking
// changes[i] = updatedValues[i].value;
oldValue = startPoint[i];
}
// if var changes has been defined (i.e. value of any list was updated)
// finding index of initial array with same value
var key = startPoint.findIndex(x => x == target.value);
// setting value of found index to previously stored value in updated list
if (key !== -1)
updatedValues[key].value = oldValue;
}
setStartingPointValues();
}
// event listeners for change of every dropdown list
const lists = document.querySelectorAll("select");
for (k = 0; k < lists.length; k++) {
lists[k].addEventListener("change", calculateNewValues, false);
}
<p>
<select name="list1" id="list1">
<option value="1" id="list1option1" selected>1</option>
<option value="2" id="list1option2">2</option>
<option value="3" id="list1option3">3</option>
</select>
</p>
<p>
<select name="list2" id="list2">
<option value="1" id="list2option1">1</option>
<option value="2" id="list2option2" selected>2</option>
<option value="3" id="list2option3">3</option>
</select>
</p>
<p>
<select name="list3" id="list3">
<option value="1" id="list3option1">1</option>
<option value="2" id="list3option2">2</option>
<option value="3" id="list3option3" selected>3</option>
</select>
</p>