[Vuejs]-Prompt before leaving page with vee-validate

I was making this more difficult than it needed to be. Just needed to add onbeforeunload event, and then set it to null when sumbmitting. Works a treat.

Updated javascript:

<script>
    window.onbeforeunload = function() {
        return true;
    };
    Vue.use(VeeValidate);
    new Vue({
        el: "#app",
        template: '#app',
        data() {
            return {
                cust_name_first: null,
                cust_id: null,
                sales_name_first: null,
            };
        },
        methods: {
            doSubmit() {
                this.$validator.validateAll().then(function(result){
                    if (!result){
                        //this means a validation failed, so exit without doing anything
                        return;
                    }
                    //here you would put your form submit stuff
                    window.onbeforeunload = null;
                    document.getElementById('webform').submit();
                });
            }
        }
    });

</script>