data() {
        return {
            sending: false,
            form: this.$inertia.form({
                name: "",
      })
};
},
methods: {
        submit() {
            this.sending = true;

            this.form.post(this.route("test"), {
                preserveScroll: true,
                onSuccess: () => (this.sending = false),
                onError: () => (this.sending = false)
            });
        }
}
mounted(){
  this.form.custom = "example".
}