SP.ClientContext (siteURL) error this.set_formDigestHandlingEnabled

When you are using Site URL to get ClientContext use 'new' keyword while define else you will see error...
this.set_formDigestHandlingEnabled


example.

$(document).ready(function () {

    //get context 
    context = new SP.ClientContext(siteURL);
    web = context.get_web();

});