js 抓取屏幕宽度设置字体大小 rem

var doc = window.document
var docEl = doc.documentElement
var tid

function refreshRem () {
var width = docEl.getBoundingClientRect().width
if (width > 540) { // 最大宽度
width = 540
}
var rem = width / 7.5 // 将屏幕宽度分成750份，1份为1rem 375屏刚好0.5px
docEl.style.fontSize = rem + 'px'
}

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

refreshRem()

(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 = 20 * (clientWidth / 320) + 'px';
        };
    if (!doc.addEventListener) return;
    win.addEventListener(resizeEvt, recalc, false);
    doc.addEventListener('DOMContentLoaded', recalc, false);
})(document, window);