I want to check, if the user is member of a special team. If he is member of the team, I want to show some tabs. If the user is not a member of this team, I want to hide the tabs.

Use following Javascript to check, weather the current user is member of the A-Team:

function CFTabs() {

var teamName = 'A-Team';

var ClientUrl = Xrm.Page.context.getClientUrl();

 checkTeam('A-Team');

function checkTeam(teamName) {

var clientURL = Xrm.Page.context.getClientUrl();

var req = new XMLHttpRequest();

var userId = Xrm.Page.context.getUserId();

 userId = userId.replace("{", "");

 userId = userId.replace("}", "");

var query = "/api/data/v8.2/systemusers(" + userId + ")?$expand=teammembership_association($select=name;$filter=name eq '" + teamName + "')";

 req.open("GET", encodeURI(clientURL + query), false);

 req.setRequestHeader("Accept", "application/json");

 req.setRequestHeader("Content-Type", "application/json;charset=utf-8");

 req.setRequestHeader("OData-MaxVersion", "4.0");

 req.setRequestHeader("OData-Version", "4.0");

req.send();

if (req.status == 200) {

var data = JSON.parse(req.response).teammembership_association;

if (data.length > 0) {

 Xrm.Page.ui.tabs.get("TAB1").setVisible(true);

 Xrm.Page.ui.tabs.get("TAB2").setVisible(true);

 Xrm.Page.ui.tabs.get("TAB3").setVisible(true);

}

else {

 Xrm.Page.ui.tabs.get("TAB1").setVisible(false);

 Xrm.Page.ui.tabs.get("TAB2").setVisible(false);

 Xrm.Page.ui.tabs.get("TAB3").setVisible(false);

}

}

}

}

You can also use array of teams:

function CFTabs() {

var teamName = ['A-Team', 'B-Team', 'C-Team', 'D-Team'];

for (i = 0; i <= teamName.length; i++) {

var ClientUrl = Xrm.Page.context.getClientUrl();

var clientURL = Xrm.Page.context.getClientUrl();

var req = new XMLHttpRequest();

var userId = Xrm.Page.context.getUserId();

 userId = userId.replace("{", "");

 userId = userId.replace("}", "");

var query = "/api/data/v8.2/systemusers(" + userId + ")?$expand=teammembership_association($select=name;$filter=name eq '" + teamName[i] + "')";

 req.open("GET", encodeURI(clientURL + query), false);

 req.setRequestHeader("Accept", "application/json");

 req.setRequestHeader("Content-Type", "application/json;charset=utf-8");

 req.setRequestHeader("OData-MaxVersion", "4.0");

 req.setRequestHeader("OData-Version", "4.0");

req.send();

var data = JSON.parse(req.response).teammembership_association;

if (data.length > 0) {

 Xrm.Page.ui.tabs.get("TAB1").setVisible(true);

 Xrm.Page.ui.tabs.get("TAB2").setVisible(true);

 Xrm.Page.ui.tabs.get("TAB3").setVisible(true);

return;

}

else {

 Xrm.Page.ui.tabs.get("TAB1").setVisible(false);

 Xrm.Page.ui.tabs.get("TAB2").setVisible(false);

 Xrm.Page.ui.tabs.get("TAB3").setVisible(false);

}

}

}