php - 基于所选选项值的表单输入值

Question

对于下面的形式

<form action ='search.php' method = 'post'>

<select name="filter">
<option id="A" value="A">A</option>
<option id="B" value="B">B</option>
</select>

<input type ='text' name="key" id ="field" value ="something that changes based on what option is selected" />

<input type ='submit' value = 'Search' />

</form>

如何根据选择的是 A 还是 B 来更改输入字段的值？我认为它必须在 javascript 中完成。我在这里和那里使用过 jquery，所以可以根据它提出建议。非常感谢!

Answer 1

您不必使用 jQuery，(但 jQuery 确实让生活更轻松):

HTML:

<form action ='search.php' method = 'post'>
    <select id="filter" name="filter">
    <option id="A" value="A">A</option>
    <option id="B" value="B">B</option>
    </select>

    <input type ='text' name="key" id ="field" value ="something that changes based on what option is selected" />

    <input type ='submit' value = 'Search' />    
</form>

Javascript:

document.getElementById('filter').onchange = function () {
    document.getElementById('field').value = event.target.value  
}

Example