Remote VideoStream not working with WebRTC

Question

EDIT: I wrote a detailed tutorial explaining how to build an simple Videochat-application including a signaling server:

Tutorial: Create your own Videochat-Applicat

Answer 1

function sharescreen(){
getScreenStream(function(screenStream) {
localpearconnection.removeTrack(localStream); 
localpearconnection.addStream(screenStream);
localpearconnection.createOffer().then(description => createdLocalDescription(description)).catch(errorHandler);
document.getElementById('localVideo').srcObject = screenStream;});}

function getScreenStream(callback) {
if (navigator.getDisplayMedia) {
    navigator.getDisplayMedia({
        video: true
    }).then(screenStream => {
        callback(screenStream);
    });
} else if (navigator.mediaDevices.getDisplayMedia) {
    navigator.mediaDevices.getDisplayMedia({
        video: true
    }).then(screenStream => {
        callback(screenStream);
    });
} else {
    getScreenId(function(error, sourceId, screen_constraints) {
        navigator.mediaDevices.getUserMedia(screen_constraints).then(function(screenStream) {
            callback(screenStream);
        });
    });
}}

The above code working for me.