sp15tax_newGroup.js

$(document).ready(function(){   
  
	var scriptbase = _spPageContextInfo.webServerRelativeUrl + "_layouts/15/";
	
	$.getScript(scriptbase + "SP.Runtime.js",
        function () {
            $.getScript(scriptbase + "SP.js", function(){
            
            	$.getScript(scriptbase + "SP.Taxonomy.js", execOperation);

            });
        }
    );

});

function execOperation(){
	
	//Current Context
    var context = SP.ClientContext.get_current();
	
    //Current Taxonomy Session
    var taxSession = SP.Taxonomy.TaxonomySession.getTaxonomySession(context);
    
    //Term Stores
    var termStores = taxSession.get_termStores();
    
    //Term Store under which to create the group.
    var termStore = termStores.getByName("Taxonomy_Dmxzz8tIBzk8wNVKQpJ+xA==");    	
	
	//New Group with name and new GUID
	var newGroup = termStore.createGroup("New Group Name","b300304a-1693-4629-a1c0-dff7bda644ff");
	
	context.load(newGroup);
		
	context.executeQueryAsync(function(){
	
  	console.log(newGroup.get_name());
   		
	},function(sender,args){
	
	console.log(args.get_message());
	
	});

}