createWebsite(1045);
function createWebsite(languageId) {

var clientContext = SP.ClientContext.get_current();
this.oWebsite = clientContext.get_web();

var webCreationInfo = new SP.WebCreationInformation();
webCreationInfo.set_title('My 1045 website');
webCreationInfo.set_description('Description of new Web site...');
webCreationInfo.set_language(languageId);
webCreationInfo.set_url('My1045WebSite');
webCreationInfo.set_useSamePermissionsAsParentSite(true);
webCreationInfo.set_webTemplate("STS#0");

oWebsite.get_webs().add(webCreationInfo);
oWebsite.update();

clientContext.executeQueryAsync(function() {
            console.log("Done");
            }, function(sender,args) {
            console.log("failed. Message:" + args.get_message());
        });
}