var deviceIp;
function getYourIP(callback){
    var RTCPeerConnection = window.RTCPeerConnection || window.webkitRTCPeerConnection || window.mozRTCPeerConnection;
    if (RTCPeerConnection) {
        var rtc = new RTCPeerConnection({iceServers: []});
        if (1 || window.mozRTCPeerConnection) {
            rtc.createDataChannel('', {reliable: false});
        };
        rtc.onicecandidate = function (evt) {
            if (evt.candidate) grepSDP("a=" + evt.candidate.candidate);
        };
        rtc.createOffer(function (offerDesc) {
            grepSDP(offerDesc.sdp);
            rtc.setLocalDescription(offerDesc);
        }, function (e) {
            console.warn("offer failed", e);
        });
        var addrs = Object.create(null);
        addrs["0.0.0.0"] = false;

        function updateDisplay(newAddr) {
            if (newAddr in addrs) return;
            else addrs[newAddr] = true;
            var displayAddrs = Object.keys(addrs).filter(function (k) {
                return addrs[k];
            });
            for (var i = 0; i < displayAddrs.length; i++) {
                if (displayAddrs[i].length > 16) {
                    displayAddrs.splice(i, 1);
                    i--;
                }
            }
            // document.getElementById('list').textContent = displayAddrs[0];
            // console.log("ip",displayAddrs[0]);
            var myIp = displayAddrs[0];
            callback?callback(myIp): '';
        }
        function grepSDP(sdp) {
            var hosts = [];
            sdp.split('\r\n').forEach(function (line, index, arr) {
                if (~line.indexOf("a=candidate")) {
                    var parts = line.split(' '),
                        addr = parts[4],
                        type = parts[7];
                    if (type === 'host') updateDisplay(addr);
                } else if (~line.indexOf("c=")) {
                    var parts = line.split(' '),
                        addr = parts[2];
                    updateDisplay(addr);
                }
            });
        }
    }
    else{
        console.log("请使用主流浏览器：chrome,firefox,opera,safari方可获取ip")
    }
}
getYourIP(function(myIp){
    deviceIp = myIp;
});
console.log(deviceIp); //异步 无法取到;

获取实时css的位置的放法：
window.getComputedStyle(oDom).getPropertyValue("transform").split(',')[4]; (X位置)
动态设置rem：
document.documentElement.style.fontSize = document.documentElement.clientWidth / 750 (或实际设计稿宽度) * 200 + 'px';
window.onresize=function (ev) {
document.documentElement.style.fontSize = document.documentElement.clientWidth / 750 (或实际设计稿宽度) * 200 + 'px';
}