移动端动态rem的计算方法 (1rem = 100px）

一 在main.js中引入 flexible.js

vue项目中 

import './assets/js/flexible'   //vue

jquery项目中 

<script src="./js/flexible.js"></script>

二 flexible.js全部代码如下

(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 && !iOS93) {
      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 > 1024) {
      width = 1024 * dpr
    }
    var rem = width / 3.75
    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'] = {}))