How to check if the user exists in a particular SharePoint group using ECMAScript

In this blog you will see how to check if the user exists in a particular SharePoint group using ECMAScript.

 

<script type="text/javascript">
ExecuteOrDelayUntilScriptLoaded(IsUserExists, "sp.js");

var group;
var users;
var ctx;
var groupCollection;
var user;
var currentuser;

function IsUserExists() {
   ctx = SP.ClientContext.get_current();
   groupCollection = ctx.get_web().get_siteGroups();
   currentuser=ctx.get_web().get_currentUser();
   group = groupCollection.getById(4103);
   ctx.load(group);
   ctx.load(currentuser);
   ctx.executeQueryAsync(Function.createDelegate(this, this.OnGetGroupSuccess), Function.createDelegate(this, OnFailure));
}

function OnGetGroupSuccess() {
    users=group.get_users();
    ctx.load(users);
    ctx.executeQueryAsync(Function.createDelegate(this, this.OnGetuserSuccess), Function.createDelegate(this, OnFailure));
}

function OnGetuserSuccess() {
    var userEnumerator = users.getEnumerator();
    while (userEnumerator.moveNext()) {
           var user = userEnumerator.get_current();
           if (user.get_id() == currentuser.get_id()) {
                   alert("User Exists")
                   break;
                }
                else
                {
                }
            }
         }

function OnFailure(sender, args) {
  alert("Failed to execute IsCurrentUserMemberOfGroup method");
}
</script>