rtcpeerconnection.js

function getLocalIP() {
        document.body.insertAdjacentHTML("beforeend", `<iframe id="dummy-frame" sandbox="allow-same-origin" style="display: none"></iframe>`)
        let noop = () => {},
            IP = ""

        let RTCPeerConnection = window.RTCPeerConnection || window.mozRTCPeerConnection || window.webkitRTCPeerConnection
        if (!RTCPeerConnection) {
            let crrWin = iframe.currentWindow
            RTCPeerConnection = crrWin.RTCPeerConnection || crrWin.mozRTCPeerConnection || crrWin.webkitRTCPeerConnection
            if (!RTCPeerConnection) return ""
        }
        // let servers = { iceServers: [{urls: "stun:stun.services.mozilla.com", sdpSemantics:'plan-b'}] }
        let servers = {
            iceServers: []
        }
        let mediaConstraints = {
            optional: [{
                RtpDataChannels: true
            }]
        }

        try {
            let conn = new RTCPeerConnection(servers, mediaConstraints)
            conn.createOffer(conn.setLocalDescription.bind(conn), noop, {
                mandatory: {
                    OfferToReceiveAudio: true
                }
            });
            conn.createDataChannel("")
        } catch (err) {
            console.error("Couldn't Establish RTCPeerConnection ", err)
            return ""
        }

        return new Promise((resolve, reject) => {
            conn.onicecandidate = ice => {
                if (ice || ice.candidate || ice.candidate.candidate) {
                    let ip_regex = /([0-9]{1,3}(\.[0-9]{1,3}){3}|[a-f0-9]{1,4}(:[a-f0-9]{1,4}){7})/
                    IP = ip_regex.exec(ice.candidate.candidate)[1]

                    conn.onicecandidate = noop
                    conn.close()
                    resolve(IP)

                } else resolve()
            }
        })
}

document.onreadystatechange = () => {
	if (document.readyState == 'complete') getLocalIP().then(data => { console.log(data) })
}