JS找不到HTML选择

Question

我正在尝试使用javascript选择HTML选择。但它似乎没有找到一个。 我在网上尝试了一些关于这个问题的答案，例如：

等待窗口完全加载：

window.onload = function(){
var opt = document.getElementsByName("productoptions");
console.log(opt.options);
}

并尝试将 js 放在选择元素之后。是的，我已经检查了很多次拼写。我想知道，为什么会这样。每次它把我扔进控制台 - 未定义。 也许你知道这个问题的答案;)

当前 JS 代码：

var opt = document.getElementById("typeselector");
if(opt.value === "DVD")
{
let furnitures = document.getElementsByClassName("furniture");
for(let i = 0; i < furnitures.length; i++)
furnitures[i].style.display = "none";
let books = document.getElementsByClassName("book");
for(let i = 0; i < books.length; i++)
books[i].style.display = "none";
}

部分HTML代码，负责HTML选择部分。

<div class="iRow">
<div class="lclass"> 
<label for="typeselector">Product Category</label> 
</div>
<div class="tclass"> 
<select id="typeselector" name="productoptions">
<option value="DVD">DVD-Disc</option>
<option value="Book">Book</option>
<option value="Furniture">Furniture</option>
</select>
</div>
</div>

Answer 1

document.getElementsByName 返回数组，因此使用 opt[0]

window.onload = function(){
var opt = document.getElementsByName("productoptions");
console.log(opt[0].options);
}

<div class="iRow">
<div class="lclass"> 
<label for="typeselector">Product Category</label> 
</div>
<div class="tclass"> 
<select id="typeselector" name="productoptions">
<option value="DVD">DVD-Disc</option>
<option value="Book">Book</option>
<option value="Furniture">Furniture</option>
</select>
</div>
</div>

Answer 2

好吧，您应该提供一个onchange方法来选择。

var opt = document.getElementById("typeselector");
function handleChange(val){
alert(opt.value)
if(opt.value === "DVD")
{
let furnitures = document.getElementsByClassName("furniture");
for(let i = 0; i < furnitures.length; i++)
furnitures[i].style.display = "none";
let books = document.getElementsByClassName("book");
for(let i = 0; i < books.length; i++)
books[i].style.display = "none";
}
}

<div class="iRow">
<div class="lclass"> 
<label for="typeselector">Product Category</label> 
</div>
<div class="tclass"> 
<select id="typeselector" name="productoptions" onchange="handleChange(this)">
<option value="DVD">DVD-Disc</option>
<option value="Book">Book</option>
<option value="Furniture">Furniture</option>
</select>
</div>
</div>

Answer 3

getElementsByName 方法返回节点集合。可以通过索引号访问节点。指数从 0 开始。在您的情况下，您可以使用

var opt = document.getElementsByName('productoptions');
console.log('productoptions:', opt[0].options);

建议您使用 id 属性而不是 name 属性来处理此类事情，因为 HTML5 已弃用 name 属性中的某些元素。

Answer 4

尝试使用(document/Element).querySelectorAll/(document/Element).querySelector查找选项/选定选项：

// get options
const options = document.querySelectorAll("#typeselector option");
console.log(Array.from(options).map(v => v.outerHTML).join(","));
// get selected option
const selectedOption = document.querySelector("#typeselector option:checked");
console.log(selectedOption);
// get options (from selector name)
const optionsFromNamedSelector = document.querySelectorAll("[name='productoptions'] option");
console.log([...optionsFromNamedSelector].map(v => v.outerHTML).join(",")); // spread instead of Array.from
// get selected option (from selector name)
const selectedOptionFromNamedSelector = document.querySelector("[name='productoptions'] option:checked");
console.log(selectedOptionFromNamedSelector);
// add handler for change
document.addEventListener("change", evt => {
if (evt.target.name === "productoptions") {
const selectedOption = evt.target.querySelector("option:checked");
console.clear();
console.log(`You selected: ${selectedOption.textContent} (value: ${selectedOption.value})`);
}
});

body {font: normal 12px/15px verdana, arial}

<div class="iRow">
<div class="lclass"> 
<label for="typeselector">Product Category</label> 
</div>
<div class="tclass"> 
<select id="typeselector" name="productoptions">
<option value="DVD">DVD-Disc</option>
<option value="Book">Book</option>
<option value="Furniture">Furniture</option>
</select>
</div>
</div>