How can i get sharepoint groupId using Javascript (JSOM)

Dear all,

I want to get SharePoint GroupId by name using JSOM, I try below code but this code throw error.

function getGroupID()
{
var groupName="DemoGroup";
var context = SP.ClientContext.get_current();  
var group = context.get_web().get_siteGroups().getByName(groupName);
context.load(group);
context.executeQueryAsync(
function() 
{
membershipGroupId = group.get_id();
console.log(membershipGroupId);
GrantPermissionForGroup
},
function(sender,args)
{
console.log(args.get_message());
}
);
}

When i run this code, i face this error,

please help me how can i get sharepoint group id.

Thanks!