javascript - if 语句未在 javascript 中执行 [始终为 else]

Question

请任何人帮忙。它总是返回其他..我想要的是，当选择第一个下拉列表时，第二个下拉列表隐藏，反之亦然

html

<form id="myform" onchange="check();" >

<select id="myselecta" >
 <option value="a1">a1</option>
 <option value="a2">a2</option>
</select>

<select id="myselectb" >
    <option value="b1">b1</option>
    <option value="b2">b</option>
</select> 

java脚本

function check() {
    var dropdown = document.getElementById('myform').value;
        if (dropdown == 'myselecta') {
        document.getElementById('myselectb').style.display = 'none';
        }
        else {
            document.getElementById('myselecta').style.display = 'none';
        }
}

Answer 1

你想完成这样的事情吗？

HTML

<select id="switch" onchange="check();">
 <option value="myselecta">myselecta</option>
 <option value="myselectb">myselectb</option>
</select>

<select id="myselecta">
 <option value="a1">a1</option>
 <option value="a2">a2</option>
</select>

<select id="myselectb">
 <option value="b1">b1</option>
 <option value="b2">b</option>
</select> 

JS

function check() {
    var dropdown = document.getElementById('switch').value;
    if (dropdown === 'myselecta') {
        document.getElementById('myselecta').style.display = 'block';
        document.getElementById('myselectb').style.display = 'none';
    } else {
        document.getElementById('myselecta').style.display = 'none';
        document.getElementById('myselectb').style.display = 'block';
    }
}

编辑

html

<select id="myselecta" onclick="check()">
 <option value="a1">a1</option>
 <option value="a2">a2</option>
</select>

<select id="myselectb" onclick="check()">
 <option value="b1">b1</option>
 <option value="b2">b</option>
</select>

JavaScript

function check() {
    if (this.id === 'myselecta') {
        document.getElementById('myselectb').style.display = 'none';
    } else {
        document.getElementById('myselecta').style.display = 'none';
    }
}