If you want to update the values of the dropdown based on the values of other dropdown. Here is the example where If I choose Chicken as my where from. My where to should display Baked potato, Mutton, fish.

<form class="foodorder hide">
                        <fieldset name="fs1" class="fs1">
                            <h1 class="fs-title">Book your food order</h1>
                            <select id="food-from">
                                <option disabled selected hidden>Where from?</option>
                                <option>veg</option>
                                <option>Pasta</option>
                                <option>Chicken/option>
                                <option>Baked potato</option>
                                <option>Mutton</option>
                                <option>fish</option>
                            </select>
                            <select id="travel-to" disabled>
                                <option disabled selected hidden>Where to?</option>
                            </select>
                    </form>

Now add this code into your js file.

var allfood = ["veg", "Pasta", "Chicken", "Baked potato", "Mutton", "fish"];

$(document).ready(function(){   

    $("#travel-from").on( "change", function( event, ui ) {
        var food = allfood.slice();

        var selectedFood = $(this).val();

        var index = cities.indexOf(selectedFood);
        for (i = index; i > -1; i--){
            food.splice(i,1);
        }
        $('#travel-to').find('option').remove();
        $('#travel-to').prop('disabled', false);

        $.each(cities, function(val, text) {
               console.log('inside change: ' +food)
                $("#travel-to").append(
                    $('<option></option>').val(val).html(text)
                );
            });
    } );
});

I hope this code will help you to implement this functionality.