Javascript 在媒体查询更改后覆盖 CSS 显示属性

Question

我有一个表格，我需要在桌面上显示它并在移动设备上隐藏它，可以选择单击一个按钮来显示它，然后单击另一个按钮将它隐藏在后者上。它看起来工作正常，但是当我选择 Button2 以在桌面上以最小化 View 隐藏表格(以模仿移动 View )并拖动浏览器以将其大小增加到桌面时，除非我刷新页面，否则表格将保持隐藏状态。

基本上，javascript 函数 close_table() 设置 display:none 覆盖 CSS display:block @min-width 481px。

有没有一种方法可以确保在增加浏览器大小时(在选择了 button2 之后)表格可见而无需刷新？

任何提示/帮助将不胜感激。

下面是示例代码

HTML:

<button id="Button1" onclick="view_table()">View table</button>
<div id="table">
    <button id="Button2” onclick="close_table()">Hide table</button>
</div>

CSS:

@media (max-width:480px){
    #table {
        display: none;
    }
    #Button1 {
        display: block;
    }
}

@media (min-width:481px){
    #table {
        display: block;
    }
    #Button1 {
        display: none;
    }
}

JS:

function view_table() {
    document.getElementById("table").style.display="block"
}
function close_table() {
    document.getElementById("table").style.display="none"
}

Answer 1

问题是，当您说 document.getElementById('table').styles.* 时，您是通过 DOM 直接在元素上设置样式，DOM 的优先级高于媒体查询通过 CSS。这意味着当再次触发媒体查询时，不会发生任何事情，因为 DOM 元素现在具有更高优先级的样式，因此 MQ 规则将被忽略。

您也不能执行通常的 .hide .show 类，因为没有办法仅通过媒体查询来添加或删除类。

这几乎剩下 EventListeners 将监听正在调整大小的窗口并执行您想要的功能。

我找到了 this article并且能够使用它来编写完成您正在寻找的功能的代码片段。

JavaScript 可以访问 window.matchMedia，这是存储文档的所有媒体相关元素的地方。简而言之，这允许我们直接在 JavaScript 中使用类似媒体查询的字符串，而不仅仅是在我们的 CSS 中.

这里有一些关于媒体查询的额外资源，可能有助于您在学习时快速浏览。

对于代码片段，单击整页让您看到调整窗口大小的样子。

Using Media Queries

Media Query types

MatchMedia()

/* Commented code on bottom is running. This is un-commented for easier readability.

'use strict'


if (matchMedia) { 
  const mq = window.matchMedia("(min-width: 481px)"); 
  mq.addListener(WidthChange); 
  WidthChange(mq); 
}

function WidthChange(mq) {
  if (mq.matches) {
    view_table() 
  } else {
    close_table()
  }
}

function view_table() {
  document.getElementById('table').style.visibility = 'visible'
  document.getElementById('button2').style.visibility = 'visible'
  document.getElementById('button1').style.visibility = 'hidden' 
}

function close_table() {
  document.getElementById('table').style.visibility = 'hidden'
  document.getElementById('button2').style.visibility = 'hidden'
  document.getElementById('button1').style.visibility = 'visible' 
}


*/

'use strict'


if (matchMedia) { // technically this is window.matchMedia, which is actually a function stored as a property on the window object. If the browser supports matchMedia then this is true. Else - no media queries regardless.

  const mq = window.matchMedia("(min-width: 481px)"); // The matchMedia() function is passed a media query string.

  mq.addListener(WidthChange);
  WidthChange(mq); // Immediately calls the new listener and pass in the mq object.
}

function WidthChange(mq) {
  // Equivalant to window.matchMedia("(min-width: 481px)").matches... .matches is a Boolean.
  if (mq.matches) {
    view_table() // If mq.matches is true ( meaning >= 481px)
  } else {
    close_table()
  }

}

function view_table() {
  document.getElementById('table').style.visibility = 'visible'
  document.getElementById('button2').style.visibility = 'visible'
  document.getElementById('button1').style.visibility = 'hidden' // You can also say display:none here on button1 to have the table move up into the spot where the button was for a cleaner look.
}

function close_table() {
  document.getElementById('table').style.visibility = 'hidden'
  document.getElementById('button2').style.visibility = 'hidden'
  document.getElementById('button1').style.visibility = 'visible' // If you do say display:none above, then this needs to beexactly what the original display property was.

}


// Note that this will update when the window go above or below the min-width.
// If you click the "view table" button  then make the window smaller
// it won't hide anything unless you went above the min-width then back down.
// This is because it's only triggered on a true or false change. If you want 
// it to be more reactive you can add more conditionals or check out MediaQueryList.change().

main {
  width: 100%;
}

table {
  width: 70%;
  border: 1px solid black;
  margin: auto;
}

.buttons {
  margin-top: 5px;
  margin-bottom: 5px;
  text-align: center;
}

<!DOCTYPE html>
<html>

<head>
  <link href="index.css" rel="stylesheet" type="text/css" />
</head>

<body>
  <main id="main">
    <div class="buttons">
      <button id="button1" onclick="view_table()">View table</button>
    </div>
    <div id="table">
      <table>
        <tr>
          <td>sample</td>
          <td>100</td>
          <td>10000</td>
        </tr>
        <tr>
          <td>sample</td>
          <td>100</td>
          <td>10000</td>
        </tr>
        <tr>
          <td>sample</td>
          <td>100</td>
          <td>10000</td>
        </tr>
      </table>
    </div>
    <div class="buttons">
      <button id="button2" onclick="close_table()">Hide table</button>
    </div>
  </main>
</body>
<script src="index.js "></script>

</html>