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js动态计算移动端rem
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‘] = {}));
js动态计算移动端rem
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