通过首先选择并选中复选框来更改选择标签

Question

我有选择标签的动态数量和一个复选框，我只需要一个简单的 JavaScript 代码 当我更改第一个选择标签并选中复选框时，所有其他选择的标签都将更改为与第一个标签相同

<input type="checkbox" id="mycheck">
<select id="first">
<option value='1'>1</option>
<option value='2'>2</option>
<option value='3'>3</option>
</select>
<select id="second">
<option value='1'>1</option>
<option value='2'>2</option>
<option value='3'>3</option>
</select>
<select id="third">
<option value='1'>1</option>
<option value='2'>2</option>
<option value='3'>3</option>
</select>
<select id="fourth">
<option value='1'>1</option>
<option value='2'>2</option>
<option value='3'>3</option>
</select>

当我更改第一个选择并选中复选框时，另一个选择更改为与第一个选择相同 谢谢提前

Answer 1

我 guss 用户想要 -> 首先更改第一个选择框，然后选中复选框以更改其余选择框

function updateSel(obj){
if(obj.checked==true){ // change only when it is checked
var selElems=document.getElementById('selectorDiv').getElementsByTagName('select') /*applies to all select elements inside div with id 'selectorDiv'*/
var val;
for(var i=0;i<selElems.length;i++){
    if(i==0)(
     val=selElems[i].value
    )
    selElems[i].value=val
}
}
}

<input type="checkbox" id="mycheck" onchange="updateSel(this)">
<div id="selectorDiv">
<select id="first">
<option value='1'>1</option>
<option value='2'>2</option>
<option value='3'>3</option>
</select>
<select id="second">
<option value='1'>1</option>
<option value='2'>2</option>
<option value='3'>3</option>
</select>
<select id="third">
<option value='1'>1</option>
<option value='2'>2</option>
<option value='3'>3</option>
</select>
<select id="fourth">
<option value='1'>1</option>
<option value='2'>2</option>
<option value='3'>3</option>
</select>
</div>