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>