JSFiddle - React, Tailwind, and code Playground

HTML

<select name="city" size="10" multiple id="city">
        <option value="0">Allen</option>
        <option value="1">Arlington</option>
        <option value="2">Aubrey</option>
        <option value="3">Bedford</option>
        <option value="4">Burleson</option>
        <option value="5">Carrollton</option>
        <option value="6">Cedar Hill</option>
        <option value="7">Commerce</option>
        <option value="8">Coppell</option>
        <option value="9">Dallas</option>
        <option value="10">Decatur</option>
    </select>
    <br />
<input name="submit" type="submit" value="Search" onclick="checkForm(); return false;"  id="search" class="search"></input>

JavaScript

function checkForm() {
    var citySelection = document.getElementById("city");
    var selectedValuesArray = getSelectValues(citySelection);
    
    if (selectedValuesArray.length) {
        console.log(selectedValuesArray.length + ' VALUES WERE SELECTED!');
    } else {
        console.log('NO VALUE WAS SELECTED...');
    }
}

function getSelectValues(select) {
  var result = [];
  var options = select && select.options;
  var opt;

  for (var i=0, iLen=options.length; i<iLen; i++) {
    opt = options[i];

    if (opt.selected) {
      result.push(opt.value || opt.text);
    }
  }
  return result;
}

var e = document.getElementById('search'); e.onclick = checkForm;