移動端(手機端)頁面自適應解決方案—rem佈局篇

假設設計妹妹給咱們的設計稿尺寸爲750 * 1340。結合網易、淘寶移動端首頁html元素上的動態font-size屬性、設計稿尺寸、前端與設計之間協做流程通常分爲下面兩種：

一 網易作法： 引入 頁面開頭處引入這段代碼。用於動態計算font-size

（function (){
       var docEl = doc.documentElement,
    isIOS = navigator.userAgent.match(/\(i[^;]+;( U;)? CPU.+Mac OS X/),
    dpr = isIOS ? Math.min(win.devicePixelRatio, 3) : 1,
    dpr = window.top === window.self ? dpr : 1, //被iframe引用時，禁止縮放
    dpr = 1,
    scale = 1 / dpr,
    resizeEvt = 'orientationchange' in window ? 'orientationchange' : 'resize';
	docEl.dataset.dpr = dpr;
	var metaEl = doc.createElement('meta');
	metaEl.name = 'viewport';
	metaEl.content = 'initial-scale=' + scale + ',maximum-scale=' + scale + ', minimum-scale=' + scale;
	docEl.firstElementChild.appendChild(metaEl);
	var recalc = function() {
	var width = docEl.clientWidth;
	if (width / dpr > 750) {
	width = 750 * dpr;
	}
	// 乘以100，px : rem = 100 : 1
	docEl.style.fontSize = 100 * (width / 750) + 'px';
	};
	recalc()
	if (!doc.addEventListener) return;
	win.addEventListener(resizeEvt, recalc, false);
  
  
  }）(document, window);
  
  <style>
       body{
	     width：750px;
		 height:640px;
	   }
	   /***
	       引入後 換成的依據
	 */
		      body{
			    width:7.5rem;
				height:6.4rem;
			  }
	  </style>
	  <script>
			 var recalc = function (){
			   var width = docEl.clientWidth;
			   if(width / dpr >750) {
				  width = 750 * dpr;
			   }
			   decEl.style.fontSize = 100* (width/750) + 'px'
		 	}
	</script>

2、淘寶作法（推薦作法，尤爲是app內嵌頁面）： 引入：頁面開頭處引入下面這段代碼，用於動態計算font-size，或者單獨放入一個文件，引入文件也能夠

; (function(win, lib) { var doc = win.document; var docEl = doc.documentElement; var metaEl = doc.querySelector('meta[name="viewport"]'); var flexibleEl = doc.querySelector('meta[name="flexible"]'); var dpr = 0; var scale = 0; var tid; var flexible = lib.flexible || (lib.flexible = {});

if (metaEl) {
    var match = metaEl.getAttribute('content').match(/initial\-scale=([\d\.]+)/);
    if (match) {
        scale = parseFloat(match[1]);
        dpr = parseInt(1 / scale);
    }
} else if (flexibleEl) {
    var content = flexibleEl.getAttribute('content');
    if (content) {
        var initialDpr = content.match(/initial\-dpr=([\d\.]+)/);
        var maximumDpr = content.match(/maximum\-dpr=([\d\.]+)/);
        if (initialDpr) {
            dpr = parseFloat(initialDpr[1]);
            scale = parseFloat((1 / dpr).toFixed(2));
        }
        if (maximumDpr) {
            dpr = parseFloat(maximumDpr[1]);
            scale = parseFloat((1 / dpr).toFixed(2));
        }
    }
}

if (!dpr && !scale) {
    var isAndroid = win.navigator.appVersion.match(/android/gi);
    var isIPhone = win.navigator.appVersion.match(/iphone/gi);
    var devicePixelRatio = win.devicePixelRatio;
    if (isIPhone) {
        // iOS下，對於2和3的屏，用2倍的方案，其他的用1倍方案
        if (devicePixelRatio >= 3 && (!dpr || dpr >= 3)) {
            dpr = 3;
        } else if (devicePixelRatio >= 2 && (!dpr || dpr >= 2)) {
            dpr = 2;
        } else {
            dpr = 1;
        }
    } else {
        // 其餘設備下，仍舊使用1倍的方案
        dpr = 1;
    }
    scale = 1 / dpr;
}

docEl.setAttribute('data-dpr', dpr);
if (!metaEl) {
    metaEl = doc.createElement('meta');
    metaEl.setAttribute('name', 'viewport');
    metaEl.setAttribute('content', 'initial-scale=' + scale + ', maximum-scale=' + scale + ', minimum-scale=' + scale + ', user-scalable=no');
    if (docEl.firstElementChild) {
        docEl.firstElementChild.appendChild(metaEl);
    } else {
        var wrap = doc.createElement('div');
        wrap.appendChild(metaEl);
        doc.write(wrap.innerHTML);
    }
}

function refreshRem() {
    var width = docEl.getBoundingClientRect().width;
    // 適配平板
    if (width / dpr > 540) {
        width = 540 * dpr;
    }
    var rem = width / 10;
    docEl.style.fontSize = rem + 'px';
    flexible.rem = win.rem = rem;
}

win.addEventListener('resize', function() {
    clearTimeout(tid);
    tid = setTimeout(refreshRem, 300);
}, false);
win.addEventListener('pageshow', function(e) {
    if (e.persisted) {
        clearTimeout(tid);
        tid = setTimeout(refreshRem, 300);
    }
}, false);

if (doc.readyState === 'complete') {
    doc.body.style.fontSize = 12 * dpr + 'px';
} else {
    doc.addEventListener('DOMContentLoaded', function(e) {
        doc.body.style.fontSize = 12 * dpr + 'px';
    }, false);
}


refreshRem();

flexible.dpr = win.dpr = dpr;
flexible.refreshRem = refreshRem;
flexible.rem2px = function(d) {
    var val = parseFloat(d) * this.rem;
    if (typeof d === 'string' && d.match(/rem$/)) {
        val += 'px';
    }
    return val;
}
flexible.px2rem = function(d) {
    var val = parseFloat(d) / this.rem;
    if (typeof d === 'string' && d.match(/px$/)) {
        val += 'rem';
    }
    return val;
}