移动端响应式js代码

最大宽度为640 1rem = 32px：
(function() {
    var b = document.documentElement,
            a = function() {
                var a = b.getBoundingClientRect().width;
                b.style.fontSize = .0625 * (640 <= a ? 640 : a) + "px"
            },
            c = null;
    window.addEventListener("resize",
            function() {
                clearTimeout(c);
                c = setTimeout(a, 300)
            });
    a()
})();

最大宽度为640 1rem = 32px：

(function() {
    var b = document.documentElement,
            a = function() {
                var a = b.getBoundingClientRect().width;
                b.style.fontSize = .005 * (640 <= a ? 640 : a) + "px"
            },
            c = null;
    window.addEventListener("resize",
            function() {
                clearTimeout(c);
                c = setTimeout(a, 300)
            });
    a()
})();

不限制最大宽度：

(function (root) {
var docEl = document.documentElement,
timer = null,
width, last;

function changeRem () {
width = docEl.getBoundingClientRect().width;
if (last === width) { return; }
last = width;
root.rem = width / 20;
if (/ZTE U930_TD/.test(navigator.userAgent)) {
root.rem = root.rem * 1.13;
}
docEl.style.fontSize = root.rem + 'px';
}

changeRem();

root.addEventListener('resize', function () {
clearTimeout(timer);
timer = setTimeout(changeRem, 300);
});

root.addEventListener('orientationchange', function () {
clearTimeout(timer);
timer = setTimeout(changeRem, 300);
});
})(window, undefined);