动态设置移动页面字体大小技术方案

设置好根结点字体大小，子节点用rem做单位，实现自适应。

一、css方案之媒体查询

设置html的font-size

@media screen and (min-width: 320px) {
    html {font-size: 14px;}
}

@media screen and (min-width: 360px) {
    html {font-size: 16px;}
}

@media screen and (min-width: 400px) {
    html {font-size: 18px;}
}

@media screen and (min-width: 440px) {
    html {font-size: 20px;}
}

@media screen and (min-width: 480px) {
    html {font-size: 22px;}
}

@media screen and (min-width: 640px) {
    html {font-size: 28px;}
}

二、js方案A

window.onload=function() {
    function reCalc() {
         var windowWidth = document.documentElement.clientWidth || window.innerWidth || document.body.clientWidth;
         // windowWidth = windowWidth > 750 ? 750 : windowWidth;
         var rootSize = 28 * (windowWidth / 375);
         var htmlNode = document.getElementsByTagName("html")[0];
         htmlNode.style.fontSize = rootSize + ‘px‘;
    }
    reCalc();
    window.addEventListener(‘resize‘, reCalc, false);
}

三、js方案B

!(function(doc, win) {
  var docEl = doc.documentElement,
  resizeEvt = ‘orientationchange‘ in window ? ‘orientationchange‘ : ‘resize‘,
  reCalc = function() {
    var clientWidth = docEl.clientWidth;
    if (!clientWidth) return;
    docEl.style.fontSize = 28 * (clientWidth / 375) + ‘px‘;
  };
  if (!doc.addEventListener) return;
  win.addEventListener(resizeEvt, reCalc, false);
  doc.addEventListener(‘DOMContentLoaded‘, reCalc, false);
})(document, window);

四、js方案C

!function(win, lib) {
  var timer,
      doc     = win.document,
      docElem = doc.documentElement,

      vpMeta   = doc.querySelector(‘meta[name="viewport"]‘),
      flexMeta = doc.querySelector(‘meta[name="flexible"]‘),

      dpr   = 0,
      scale = 0,

      flexible = lib.flexible || (lib.flexible = {});

  // 设置了 viewport meta
  if (vpMeta) {
    console.warn("将根据已有的meta标签来设置缩放比例");
    var initial = vpMeta.getAttribute("content").match(/initial\-scale=([\d\.]+)/);

    if (initial) {
        scale = parseFloat(initial[1]); // 已设置的 initialScale
        dpr = parseInt(1 / scale);      // 设备像素比 devicePixelRatio
    }
  }
  // 设置了 flexible Meta
  else if (flexMeta) {
    var flexMetaContent = flexMeta.getAttribute("content");
    if (flexMetaContent) {

      var initial = flexMetaContent.match(/initial\-dpr=([\d\.]+)/),
          maximum = flexMetaContent.match(/maximum\-dpr=([\d\.]+)/);

      if (initial) {
        dpr = parseFloat(initial[1]);
        scale = parseFloat((1 / dpr).toFixed(2));
      }

      if (maximum) {
        dpr = parseFloat(maximum[1]);
        scale = parseFloat((1 / dpr).toFixed(2));
      }
    }
  }

  // viewport 或 flexible
  // meta 均未设置
  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;
  }

  docElem.setAttribute("data-dpr", dpr);

  // 插入 viewport meta
  if (!vpMeta) {
    vpMeta = doc.createElement("meta");

    vpMeta.setAttribute("name", "viewport");
    vpMeta.setAttribute("content",
        "initial-scale=" + scale + ", maximum-scale=" + scale + ", minimum-scale=" + scale + ", user-scalable=no");

    if (docElem.firstElementChild) {
      docElem.firstElementChild.appendChild(vpMeta)
    } else {
      var wrap = doc.createElement("div");
      wrap.appendChild(vpMeta);
      doc.write(wrap.innerHTML);
    }
  }

  function setFontSize() {
    var winWidth = docElem.getBoundingClientRect().width;

    if (winWidth / dpr > 540) {
        (winWidth = 540 * dpr);
    }

    // 根节点 fontSize 根据宽度决定
    var baseSize = winWidth / 10;

    docElem.style.fontSize = baseSize + "px";
    flexible.rem = win.rem = baseSize;
  }

  // 调整窗口时重置
  win.addEventListener("resize", function() {
    clearTimeout(timer);
    timer = setTimeout(setFontSize, 300);
  }, false);

  // 方向改变时重置
  win.addEventListener("orientationchange", function() {
    clearTimeout(timer);
    timer = setTimeout(setFontSize, 300);
  }, false);

  // 从浏览器读取缓存时触发，pageshow每次加载页面时触发。
  win.addEventListener("pageshow", function(e) {
    if (e.persisted) {
      clearTimeout(timer);
      timer = setTimeout(setFontSize, 300);
    }
  }, false);

  // 设置基准字体
  if ("complete" === doc.readyState) {
    doc.body.style.fontSize = 12 * dpr + "px";
  } else {
    doc.addEventListener("DOMContentLoaded", function() {
      doc.body.style.fontSize = 12 * dpr + "px";
    }, false);
  }

  setFontSize();

  flexible.dpr = win.dpr = dpr;

  flexible.refreshRem = setFontSize;

  flexible.rem2px = function(d) {
    var c = parseFloat(d) * this.rem;
    if (typeof d === "string" && d.match(/rem$/)) {
        c += "px";
    }
    return c;
  };

  flexible.px2rem = function(d) {
    var c = parseFloat(d) / this.rem;

    if (typeof d === "string" && d.match(/px$/)) {
        c += "rem";
    }
    return c;
  }
}(window, window.lib || (window.lib = {}));