JSFiddle - React, Tailwind, and code Playground

HTML

<form>
    <select class="country" name="country" id="countryid">
        <option value="usa" selected="selected">USA</option>
        <option value="canada">Canada</option>
        <option value="japan">Japan</option>
        <option value="china">China</option>
    </select>
</form>

JavaScript

var param1var = "china"//getQueryVariable("country");

function displayresult() {
    document.getElementById("countryid").value= param1var; 
}


function getQueryVariable(variable) {
    var query = window.location.search.substring(1);
    var vars = query.split("&");
    for (var i = 0; i < vars.length; i++) {
        var pair = vars[i].split("=");
        if (pair[0] == variable) {
            return pair[1];
        }
    }
}
window.onload=function(){
    displayresult();
}