how to set first element of select2 jquery as default?

THE FOLLOWING CODE IS JUST PSEUDO CODE!

It is just an example to show you how I got 2 different examples and combined in a possible solution.

 protected afterLoadEntity() {
            super.afterLoadEntity();
            // fill next number in new record mode
            if (this.isNew())
                this.form.YourFruitComboField = Northwind.FruitRow.getLookup().items.[0].FruitID
        }

protected afterLoadEntity() {
       super.afterLoadEntity();

       if (this.isNew()) {
           this.form.YourField.value = this.form.YourField.get_items()[0].id;
           this.form.YourField.element.triggerHandler("change"); //if there is some change handler you've set
    }
 }