js动态计算rem

来源：互联网发布：广州网络推广公司编辑：程序博客网时间：2024/04/28 10:36

在做移动端web app的时候，众所周知，移动设备分辨率五花八门，虽然我们可以通过CSS3的media query来实现适配，例如下面这样：

 1 html { 2         font-size : 20px; 3     } 4     @media only screen and (min-width: 401px){ 5         html { 6             font-size: 25px !important; 7         } 8     } 9     @media only screen and (min-width: 428px){10         html {11             font-size: 26.75px !important;12         }13     }14     @media only screen and (min-width: 481px){15         html {16             font-size: 30px !important; 17         }18     }19     @media only screen and (min-width: 569px){20         html {21             font-size: 35px !important; 22         }23     }24     @media only screen and (min-width: 641px){25         html {26             font-size: 40px !important; 27         }28     }

但是这种做法并不能适配所有设备，于是就有了实现全适配的JS解决方案，例如下面这样:

 1  ;(function (doc, win, undefined) { 2           var docEl = doc.documentElement, 3             resizeEvt = 'orientationchange' in win? 'orientationchange' : 'resize', 4             recalc = function () { 5               var clientWidth = docEl.clientWidth; 6               if (clientWidth === undefined) return; 7               docEl.style.fontSize = 20 * (clientWidth / 320) + 'px'; 8             }; 9           if (doc.addEventListener === undefined) return;10           win.addEventListener(resizeEvt, recalc, false);11           doc.addEventListener('DOMContentLoaded', recalc, false)12         })(document, window);13

另外附上淘宝移动端适配解决方案flexible.js源码:

  1 ;(function(win, lib) {  2     var doc = win.document;  3     var docEl = doc.documentElement;  4     var metaEl = doc.querySelector('meta[name="viewport"]');  5     var flexibleEl = doc.querySelector('meta[name="flexible"]');  6     var dpr = 0;  7     var scale = 0;  8     var tid;  9     var flexible = lib.flexible || (lib.flexible = {}); 10      11     if (metaEl) { 12         //将根据已有的meta标签来设置缩放比例 13         var match = metaEl.getAttribute('content').match(/initial\-scale=([\d\.]+)/); 14         if (match) { 15             scale = parseFloat(match[1]); 16             dpr = parseInt(1 / scale); 17         } 18     } else if (flexibleEl) { 19         var content = flexibleEl.getAttribute('content'); 20         if (content) { 21             var initialDpr = content.match(/initial\-dpr=([\d\.]+)/); 22             var maximumDpr = content.match(/maximum\-dpr=([\d\.]+)/); 23             if (initialDpr) { 24                 dpr = parseFloat(initialDpr[1]); 25                 scale = parseFloat((1 / dpr).toFixed(2));     26             } 27             if (maximumDpr) { 28                 dpr = parseFloat(maximumDpr[1]); 29                 scale = parseFloat((1 / dpr).toFixed(2));     30             } 31         } 32     } 33  34     if (!dpr && !scale) { 35         var isAndroid = win.navigator.appVersion.match(/android/gi); 36         var isIPhone = win.navigator.appVersion.match(/iphone/gi); 37         var devicePixelRatio = win.devicePixelRatio; 38         if (isIPhone) { 39             // iOS下，对于2和3的屏，用2倍的方案，其余的用1倍方案 40             if (devicePixelRatio >= 3 && (!dpr || dpr >= 3)) {                 41                 dpr = 3; 42             } else if (devicePixelRatio >= 2 && (!dpr || dpr >= 2)){ 43                 dpr = 2; 44             } else { 45                 dpr = 1; 46             } 47         } else { 48             // 其他设备下，仍旧使用1倍的方案 49             dpr = 1; 50         } 51         scale = 1 / dpr; 52     } 53  54     docEl.setAttribute('data-dpr', dpr); 55     if (!metaEl) { 56         metaEl = doc.createElement('meta'); 57         metaEl.setAttribute('name', 'viewport'); 58         metaEl.setAttribute('content', 'initial-scale=' + scale + ', maximum-scale=' + scale + ', minimum-scale=' + scale + ', user-scalable=no'); 59         if (docEl.firstElementChild) { 60             docEl.firstElementChild.appendChild(metaEl); 61         } else { 62             var wrap = doc.createElement('div'); 63             wrap.appendChild(metaEl); 64             doc.write(wrap.innerHTML); 65         } 66     } 67  68     function refreshRem(){ 69         var width = docEl.getBoundingClientRect().width; 70         if (width / dpr > 540) { 71             width = 540 * dpr; 72         } 73         var rem = width / 10; 74         docEl.style.fontSize = rem + 'px'; 75         flexible.rem = win.rem = rem; 76     } 77  78     win.addEventListener('resize', function() { 79         clearTimeout(tid); 80         tid = setTimeout(refreshRem, 300); 81     }, false); 82     win.addEventListener('pageshow', function(e) { 83         if (e.persisted) { 84             clearTimeout(tid); 85             tid = setTimeout(refreshRem, 300); 86         } 87     }, false); 88  89     if (doc.readyState === 'complete') { 90         doc.body.style.fontSize = 12 * dpr + 'px'; 91     } else { 92         doc.addEventListener('DOMContentLoaded', function(e) { 93             doc.body.style.fontSize = 12 * dpr + 'px'; 94         }, false); 95     } 96      97  98     refreshRem(); 99 100     flexible.dpr = win.dpr = dpr;101     flexible.refreshRem = refreshRem;102     flexible.rem2px = function(d) {103         var val = parseFloat(d) * this.rem;104         if (typeof d === 'string' && d.match(/rem$/)) {105             val += 'px';106         }107         return val;108     }109     flexible.px2rem = function(d) {110         var val = parseFloat(d) / this.rem;111         if (typeof d === 'string' && d.match(/px$/)) {112             val += 'rem';113         }114         return val;115     }116 117 })(window, window['lib'] || (window['lib'] = {}));

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