JS找不到HTMLselect

Question

我正在尝试 select HTML select 和 javascript。不过好像找不到了。我已经在网上尝试了几个关于这个问题的答案，例如：

等待 window 完全加载：

window.onload = function(){
    var opt = document.getElementsByName("productoptions");

    console.log(opt.options);
}

并尝试将 js 放在 select 元素之后。是的，我已经多次检查拼写。我想知道，为什么会这样。每次它都把我扔进控制台时——未定义。也许你知道答案 ;)

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HTMLselect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 returns 数组所以使用 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

嗯，你应该为 select 提供一个 onchange 方法。

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

尝试使用 (document/Element).querySelectorAll/(document/Element).querySelector 找到 options/selected 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>

Answer 4

getElementsByName 方法returns 节点集合。可以通过索引号访问节点。索引从 0 开始。在您的情况下，您可以使用

访问 select 元素

var opt = document.getElementsByName('productoptions');

console.log('productoptions:', opt[0].options);

建议您使用 id 属性而不是 name 属性来处理这些事情，因为 HTML5 已经弃用了 name 属性中的一些元素。

JS找不到HTMLselect

JS can't find HTML select

javascript

html

dom

dom-manipulation