将从combobox获得的javascript变量传递给php，而无需重定向到另一页面

Question

I get a value from combobox using javascript and I need it to make a query and fill another combobox from data fron the database.

This is how I get the value:

<select name="state" onchange="getValue(this)">
                <option value="0">Provincia</option>
                <option value="1">San José</option>
                <option value="2">Alajuela</option>
                <option value="3">Cartago</option>
                <option value="4">Heredia</option>
                <option value="5">Guanacaste</option>
                <option value="6">Puntarenas</option>
                <option value="7">Limón</option>
              </select>

              <script>
                function getValue(obj){
                   //Pass value to php
                    alert(obj.value);
                }

I want to put the value within a variable without refreshing nor redirecting to another page

Answer 1

You need to use AJAX to send your data from JavaScript to PHP. AJAX stands for Asynchronous JavaScript and XML and basically lets you request server side code asynchronously. You can also send data along with your asynchronous request:

let url; //your filepath to your php script
let param; //the value you want to send along
var xhttp = new XMLHttpRequest();
xhttp.onreadystatechange = function() {
  if (this.readyState == 4 && this.status == 200) {
    //do something with the request
  }
};
xhttp.open("POST", url, true);
xhttp.send(param);