JSFiddle - React, Tailwind, and code Playground

HTML

<input type="text" size="2" id="selectVal"/>
<button onclick="setSelect()">Set the select</button>
<select id="mySelect">
    <option value="0">Select an option</option>
    <option value="1">A</option>
    <option value="2">B</option>
    <option value="3">C</option>
    <option value="4">D</option>
</select>

JavaScript

$(document).ready(function(){
$("#mySelec").change(function(){
if(("#mySelect").val()="1")){
alert("test");
}
else if (("#mySelect").val()="2")){
}else{
alert("test");
}$("#mySelect").css("display","3")
 alert("test");
}


});

});