fetch-php.js

// SELECT ON CHANGE VALUES FETCHING TO PHP

document.querySelectorAll(`select.collect`).forEach(dropdown =>
  dropdown.addEventListener(`change`, (e) => {

    // GET VALUES
    
    let value = e.target.value;
    let text = dropdown.options[dropdown.selectedIndex].text;
    let price = dropdown.options[dropdown.selectedIndex].getAttribute(`attr-price`);
    let name = e.target.name;
    let data = {
      name: name,
      value: value,
      text: text,
      price: price,
    };

    // FETCH

    fetch('response-ajax.php', {
      method : 'POST',
      headers: {
        'Content-Type': 'application/json',
      },
      body: JSON.stringify(data)
    })
    .then(response => response.text())
    .then(text => {

      // TRY RESPONSE TYPE
      
      try {
        // JSON
        let data = JSON.parse(text);
        console.log(`JSON:`);
        console.log(data)
      } catch(err) {
        // NOT JSON
        console.log(`NOT JSON:`);
        console.log(text)
      }

    })

  })
);