移动端字体大小随设置变化

function fixRem(){
    var windowWidth =  document.documentElement.clientWidth || window.innerWidth || document.body.clientWidth;
    windowWidth = windowWidth > 640 ? 640 : windowWidth;
    var rootSize = 20 * ( windowWidth / 320);
    var htmlNode = document.getElementsByTagName("html")[0];
    htmlNode.style.fontSize = rootSize+‘px‘;
}
fixRem();
window.addEventListener(‘resize‘, fixRem, false);