JavaScript根据CSS的Media Queries来判断浏览设备的方法_html/css_WEB-ITnose
CSS 部分
首先随便新建一个用来做判断的类,然后通过 Media Queries 来对这个类的 z-index 属性赋予不同的值。这个类仅作为 JavaScript 读取使用,所以需要将其移出屏幕窗口,让浏览者不可见以免引起意外情况。
作为演示,下面代码设置了四种设备状态:桌面普通版、小屏幕桌面版、平板电脑版和手机版。
/* default state */.state-indicator { position: absolute; top: -999em; left: -999em; z-index: 1;} /* small desktop */@media all and (max-width: 1200px) { .state-indicator { z-index: 2; }} /* tablet */@media all and (max-width: 1024px) { .state-indicator { z-index: 3; }} /* mobile phone */@media all and (max-width: 768px) { .state-indicator { z-index: 4; }}
JavaScript 判断
CSS 已经就位了,那么就需要用 JavaScript 来生成了一个临时的 DOM 对象,然后为它设置对应的类,然后再读取这个对象的 z-index 值。原生的写法如下:
// Create the state-indicator elementvar indicator = document.createElement('div');indicator.className = 'state-indicator';document.body.appendChild(indicator); // Create a method which returns device statefunction getDeviceState() { return parseInt(window.getComputedStyle(indicator).getPropertyValue('z-index'), 10);}getDeviceState() 函数返回的就是 z-index 的值,为了增强一下可读性,可以用 switch 函数来规范输出一下: function getDeviceState() { switch(parseInt(window.getComputedStyle(indicator).getPropertyValue('z-index'), 10)) { case 2: return 'small-desktop'; break; case 3: return 'tablet'; break; case 4: return 'phone'; break; default: return 'desktop'; break; }}
这样,就可以用一下代码来判断设备状态,然后执行相应的 JavaScript 代码:
if(getDeviceState() == 'tablet') { // 平板电脑下执行的 JavaScript 代码}
这里如果你使用的是 jQuery,直接使用下面代码就可以了:
$(function(){ $('body').append('<div class="state-indicator"></div>'); function getDeviceState() { switch(parseInt($('.state-indicator').css('z-index'),10)) { case 2: return 'small-desktop'; break; case 3: return 'tablet'; break; case 4: return 'phone'; break; default: return 'desktop'; break; } } console.log(getDeviceState()); $('.state-indicator').remove();});

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