如何使用JavaScript更改元素的类？ [英] How can I change an element's class with JavaScript?

问题描述

如何使用JavaScript响应 onclick 事件来更改HTML元素的类？

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

推荐答案

现代HTML5更改类的技术

现代浏览器已添加 classList ，它提供了一些无需使用库即可更轻松地操作类的方法：

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，尽管有 shim 将其支持添加到IE8和IE9，可从此页面。不过，它越来越受支持。

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） ，以下示例使用-当然，您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 this --但是，对此进行详细讨论超出了答案的范围。

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，请附加一个空间和新的类名，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";

要从元素中删除类：

要在元素上删除单个类而不影响其他潜在类，则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 */

对该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 标志告诉替换为r如果需要多次添加类名，请根据需要重复执行。

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

上面用于删除类的正则表达式也可以用作检查特定类是否存在的方法：

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)/) )

虽然可以直接在HTML事件属性内编写JavaScript（例如 onclick = this.className + ='MyClass' ）不建议这样做。尤其是在大型应用程序上，通过将HTML标记与JavaScript交互逻辑分离，可以实现更具可维护性的代码。

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.

要实现这一目标的第一步是创建一个函数，然后调用该函数在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>

_{（不需要在脚本标签中包含此代码，这是只是为了简化示例，将JavaScript包含在不同的文件中可能更合适。）}

第二步是移动HTML中的onclick事件，然后进入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在HTML加载完成之后-如果不执行此操作，则调用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.)

以上代码都是标准JavaScript，但是很常见练习使用框架或库来简化常见任务，并受益于在编写代码时可能不会想到的固定错误和边缘情况。

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〜50 KB的框架来简单地更改类是过大的，但是，如果您正在做大量的JavaScript工作，或者可能有不寻常的跨浏览器行为，则值得考虑。

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，库是为特定任务而设计的一组工具，而fr amework通常包含多个库并执行完整的任务。）

上面的示例已在下面使用 jQuery ，可能是最常用的JavaScript库（尽管还有其他值得研究的库）。

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 $ 是jQuery对象。）

(Note that $ here is the jQuery object.)

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

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

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

此外，jQuery提供了一种捷径，用于添加不适用的类，或删除适用的类：

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，不需要ID：

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

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