探讨移动端布局适配方案

//以750px设计稿为例,物理像素是375px.设置div宽度为整个容器宽度一半
html{font-size:12px}
div{width:375/2/12 rem}

<script>
        (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) {
                //        console.warn(‘将根据已有的meta标签来设置缩放比例‘);
                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，对于2和3的屏，用2倍的方案，其余的用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 {
                    // 其他设备下，仍旧使用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;

                if (width / dpr > 768) {
                    width = 768 * dpr;
                }
                var rem = width / 7.5;
                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;
            }

        })(window, window[‘lib‘] || (window[‘lib‘] = {}));
    </script>