js 抓取螢幕寬度設定字型大小 rem

var doc = window.document

var docEl = doc.documentElement

var tid

function refreshRem () {

var width = docEl.getBoundingClientRect().width

if (width > 540) { // 最大寬度

width = 540

}

var rem = width / 7.5 // 将螢幕寬度分成750份，1份為1rem 375屏剛好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)

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);