所以基本上我想要实现的是当我更改选择时使输入的占位符发生变化。第一个输入成功更改，但与第二个输入似乎不一样。下面是我正在使用的代码:
function onChange(fromOrTo) {
if (fromOrTo = 'from') {
document.getElementById("from").placeholder = document.getElementById("selectFrom").value;
} else if (fromOrTo = 'to') {
document.getElementById("to").placeholder = document.getElementById("selectTo").value;
}
}<body>
<div id="sect">
<section>
<select onchange="onChange('from')" id="selectFrom">
<option value="Celcius">Celcius</option>
<option value="Farenheit">Farenheit</option>
<option value="Kelvin">Kelvin</option>
<option value="Reamur">Reamur</option>
</select>
<span class="toText">to</span>
<select onchange="onChange('to')" id="selectTo">
<option value="Celcius">Celcius</option>
<option value="Farenheit">Farenheit</option>
<option value="Kelvin">Kelvin</option>
<option value="Reamur">Reamur</option>
</select>
</section>
<section>
<input type="text" id="from">
<span id="toText">to</span>
<input type="text" id="to">
</section>
</div>
</body>最佳答案
你只需要比较===而不是=
function onChange(fromOrTo) {
if (fromOrTo === 'from') {
document.getElementById("from").placeholder = document.getElementById("selectFrom").value;
} else if (fromOrTo === 'to') {
document.getElementById("to").placeholder = document.getElementById("selectTo").value;
}
}<body>
<div id="sect">
<section>
<select onchange="onChange('from')" id="selectFrom">
<option value="Celcius">Celcius</option>
<option value="Farenheit">Farenheit</option>
<option value="Kelvin">Kelvin</option>
<option value="Reamur">Reamur</option>
</select>
<span class="toText">to</span>
<select onchange="onChange('to')" id="selectTo">
<option value="Celcius">Celcius</option>
<option value="Farenheit">Farenheit</option>
<option value="Kelvin">Kelvin</option>
<option value="Reamur">Reamur</option>
</select>
</section>
<section>
<input type="text" id="from">
<span id="toText">to</span>
<input type="text" id="to">
</section>
</div>
</body>关于javascript - 输入的占位符不会从 <select> 改变，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/49061769/