Select multiple options in dropdown list and add to url

<form action="" method="GET" id="myForm">
    <select name="channel" id="0" onChange="changeURL()">
        <option value="" selected disabled>Choose Channel</option>
        <option value="facebook-ads">Facebook ads</option>
        <option value="instagram-ads">Instagram ads</option>
    </select>
    <select name="brand" id="1" onChange="changeURL()">
        <option value="" selected disabled>Choose Brand</option>
        <option value="brand-1">brand 1</option>
        <option value="brand-2">brand 2</option>
        <option value="brand-3">brand 3</option>
    </select>
</form>
<p id="test"></p>
<script>
// Initialize the filters array
var filters = [];

// Initialize filters with any pre-selected values on page load
document.addEventListener("DOMContentLoaded", function() {
    // Get all select elements
    var selects = document.querySelectorAll('select');
    
    // Initialize the filters array with the correct size
    filters = new Array(selects.length).fill("");
    
    // Check for any pre-selected options
    selects.forEach(function(select) {
        if (select.selectedIndex > 0) { // If something is selected (not the disabled option)
            filters[select.id] = select.value;
        }
    });
    
    // Update URL on initial load
    changeURL();
});

function changeURL() {
    var yourUrl = "https://yourdomain.com"; // Base URL
    var queryParams = [];
    
    // Update the current changed value
    var selects = document.querySelectorAll('select');
    selects.forEach(function(select) {
        filters[select.id] = select.value;
    });
    
    // Build query parameters, only including valid values
    selects.forEach(function(select) {
        var paramName = select.name;
        var paramValue = filters[select.id];
        
        // Only add to URL if there's a valid value
        if (paramValue && paramValue !== "" && paramValue !== "undefined") {
            queryParams.push(paramName + "=" + paramValue);
        }
    });
    
    // Add the query string if we have parameters
    if (queryParams.length > 0) {
        yourUrl += "?" + queryParams.join("&");
    }
    
    // Display the result
    document.getElementById("test").innerHTML = yourUrl;
}
</script>