Home Web Front-end HTML Tutorial JavaScript根据CSS的Media Queries来判断浏览设备的方法_html/css_WEB-ITnose

JavaScript根据CSS的Media Queries来判断浏览设备的方法_html/css_WEB-ITnose

Jun 24, 2016 am 11:18 AM

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;  }}
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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;  }}
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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}
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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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