如何用JavaScript更改元素的类？ [英] How to change an element's class with JavaScript?

问题描述

如何使用JavaScript更改HTML元素的类以响应 onClick 事件？

How can I change a class of an HTML element in response to an onClick event using JavaScript?

推荐答案

用于更改班级的现代HTML5技术

现代浏览器添加了 classList ，它提供了一些方法，可以在不需要库的情况下更轻松地操作类：

Modern HTML5 Techniques for changing classes

Modern browsers have added classList which provides methods to make it easier to manipulate classes without needing a library:

document.getElementById("MyElement").classList.add('MyClass');

document.getElementById("MyElement").classList.remove('MyClass');

if ( document.getElementById("MyElement").classList.contains('MyClass') )

document.getElementById("MyElement").classList.toggle('MyClass');

不幸的是，这些在v10之前的Internet Explorer中不起作用，尽管有一个 shim 将其支持添加到IE8和IE9，可从此页面。但是，越来越多的支持。

Unfortunately, these do not work in Internet Explorer prior to v10, though there is a shim to add support for it to IE8 and IE9, available from this page. It is, though, getting more and more supported.

选择元素的标准JavaScript方法是使用 document.getElementById（Id） ，这是以下示例使用的内容 - 您当然可以通过其他方式获取元素，并且在正确的情况下可以简单地使用此 - 但是，详细说明这一点超出了答案的范围。

The standard JavaScript way to select an element is using document.getElementById("Id"), which is what the following examples use - you can of course obtain elements in other ways, and in the right situation may simply use this instead - however, going into detail on this is beyond the scope of the answer.

要用一个或多个新类替换所有现有类，设置className属性：

To replace all existing classes with one or more new classes, set the className attribute:

document.getElementById("MyElement").className = "MyClass";

（您可以使用以空格分隔的列表来应用多个类。）

(You can use a space-delimited list to apply multiple classes.)

要向元素添加类，而不删除/影响现有值，请附加一个空格和新的类名，如下所示：

To add a class to an element, without removing/affecting existing values, append a space and the new classname, like so:

document.getElementById("MyElement").className += " MyClass";

从元素中删除一个类：

要删除单个类到元素，而不影响其他可能的类，需要简单的正则表达式替换：

To remove a class from an element:

To remove a single class to an element, without affecting other potential classes, a simple regex replace is required:

document.getElementById("MyElement").className =
   document.getElementById("MyElement").className.replace
      ( /(?:^|\s)MyClass(?!\S)/g , '' )
/* Code wrapped for readability - above is all one statement */

这个正则表达式的解释如下：

An explanation of this regex is as follows:

(?:^|\s) # Match the start of the string, or any single whitespace character

MyClass  # The literal text for the classname to remove

(?!\S)   # Negative lookahead to verify the above is the whole classname
         # Ensures there is no non-space character following
         # (i.e. must be end of string or a space)

g 标志te如果已经多次添加类名，则将替换为需要重复。

The g flag tells the replace to repeat as required, in case the class name has been added multiple times.

上面用于删除类的相同正则表达式也可用于检查特定类是否存在：

The same regex used above for removing a class can also be used as a check as to whether a particular class exists:

if ( document.getElementById("MyElement").className.match(/(?:^|\s)MyClass(?!\S)/) )

虽然可以在HTML事件属性中直接编写JavaScript（例如 onclick =this.className + ='MyClass'）这是不推荐的行为。特别是在较大的应用程序中，通过将HTML标记与JavaScript交互逻辑分离，可以实现更易维护的代码。

Whilst it is possible to write JavaScript directly inside the HTML event attributes (such as onclick="this.className+=' MyClass'") this is not recommended behaviour. Especially on larger applications, more maintainable code is achieved by separating HTML markup from JavaScript interaction logic.

实现这一目标的第一步是创建一个函数，并调用函数在onclick属性中，例如：

The first step to achieving this is by creating a function, and calling the function in the onclick attribute, for example:

<script type="text/javascript">
    function changeClass(){
        // Code examples from above
    }
</script>
...
<button onclick="changeClass()">My Button</button>

_{（脚本标签中不需要此代码，这是仅仅为了简洁起见，将JavaScript包含在一个不同的文件中可能更合适。）}

第二步是移动onclick事件从HTML到JavaScript，例如使用 addEventListener

The second step is to move the onclick event out of the HTML and into JavaScript, for example using addEventListener

<script type="text/javascript">
    function changeClass(){
        // Code examples from above
    }

    window.onload = function(){
        document.getElementById("MyElement").addEventListener( 'click', changeClass);
    }
</script>
...
<button id="MyElement">My Button</button>

（请注意，window.onload部分是必需的，以便执行该函数的内容 HTML完成加载后 - 如果没有这个，调用JavaScript代码时MyElement可能不存在，因此该行将失败。）

(Note that the window.onload part is required so that the contents of that function are executed after the HTML has finished loading - without this, the MyElement might not exist when the JavaScript code is called, so that line would fail.)

以上代码全部采用标准JavaScript，但它很常见练习使用框架或库来简化常见任务，以及在编写代码时可能没有想到的修复错误和边缘情况。

The above code is all in standard JavaScript, however it is common practise to use either a framework or a library to simplify common tasks, as well as benefit from fixed bugs and edge cases that you might not think of when writing your code.

虽然有些人认为添加一个~50  KB框架来简单地改变一个类就太过分了，如果你正在做大量的JavaScript工作，或者任何可能有不寻常的跨浏览器行为的东西，那么值得考虑。

Whilst some people consider it overkill to add a ~50 KB framework for simply changing a class, if you are doing any substantial amount of JavaScript work, or anything that might have unusual cross-browser behaviour, it is well worth considering.

（非常粗略地说，库是为特定任务设计的一组工具，而fr是amework通常包含多个库并执行一整套职责。）

上面的示例已使用 jQuery ，可能是最常用的JavaScript库（虽然还有其他一些值得研究）。

The examples above have been reproduced below using jQuery, probably the most commonly used JavaScript library (though there are others worth investigating too).

（注意 $ 这里是jQuery对象。）

(Note that $ here is the jQuery object.)

$('#MyElement').addClass('MyClass');

$('#MyElement').removeClass('MyClass');

if ( $('#MyElement').hasClass('MyClass') )

此外，jQuery提供了一个快捷方式，用于添加一个类，如果它不适用，或者删除一个类：

In addition, jQuery provides a shortcut for adding a class if it doesn't apply, or removing a class that does:

$('#MyElement').toggleClass('MyClass');

$('#MyElement').click(changeClass);

或者，无需ID：

$(':button:contains(My Button)').click(changeClass);

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