flexible.js

/**
 * Created by hjx on 2018/6/22.
 */
(function(designWidth, maxWidth) {
  var doc = document,
    win = window,
    docEl = doc.documentElement,
    remStyle = document.createElement("style"),
    tid;

  function refreshRem() {
    var width = docEl.getBoundingClientRect().width;
    maxWidth = maxWidth || 540;
    width>maxWidth && (width=maxWidth);
    var rem = width * 100 / designWidth;
    remStyle.innerHTML = 'html{font-size:' + rem + 'px;}';
  }

  if (docEl.firstElementChild) {
    docEl.firstElementChild.appendChild(remStyle);
  } else {
    var wrap = doc.createElement('div')
    wrap.appendChild(remStyle)
    doc.write(wrap.innerHTML)
    wrap = null
  }
  // 要等 wiewport 设置好后才能执行 refreshRem，不然 refreshRem 会执行2次；
  refreshRem()

  win.addEventListener('resize', function( ) {
    clearTimeout(tid) // 防止执行两次
    tid = setTimeout(refreshRem, 300);
  }, false)

  win.addEventListener("pageshow", function(e) {
    if (e.persisted) { // 浏览器后退的时候重新计算
      clearTimeout(tid);
      tid = setTimeout(refreshRem, 300);
    }
  }, false);

  if (doc.readyState === "complete") {
    doc.body.style.fontSize = "16px";
  } else {
    doc.addEventListener("DOMContentLoaded", function(e) {
      doc.body.style.fontSize = "16px";
    }, false);
  }
})(750, 750);