rem

/**
 * @example 1rem=100px
 */
!(function (doc, win) {
    var docele = doc.documentelement,
        resizeevent = 'orientationchange' in window ? 'orientationchange' : 'resize',
        recalc = function () {
            var clientwidth = docele.clientwidth;
            if (!clientwidth) return;
            // 750为设计稿尺寸
            docele.style.fontsize = clientwidth >= 750 ? '100px' : 100 * (clientwidth / 750) + 'px'
        };
    if (!doc.addeventlistener) return;
    win.addeventlistener(resizeevent, recalc, false);
    doc.addeventlistener('domcontentloaded', recalc, false);
})(document, window);