Get selected value/text from Select on change

Question

Use either JavaScript or jQuery for this.

Using JavaScript

<script>
function val() {
    d = document.getElementById("select_id").value;
    alert(d);
}
</script>

<select onchange="val()" id="select_id">

Using jQuery

$('#select_id').change(function(){
    alert($(this).val());
})

If you're googling this, and don't want the event listener to be an attribute, use:

document.getElementById('my-select').addEventListener('change', function() {
  console.log('You selected: ', this.value);
});

<select id="my-select">
  <option value="1">One</option>
  <option value="2">Two</option>
  <option value="3">Three</option>
</select>

function test(a) {
    var x = (a.value || a.options[a.selectedIndex].value);  //crossbrowser solution =)
    alert(x);
}

<select onchange="test(this)" id="select_id">
    <option value="0">-Select-</option>
    <option value="1">Communication</option>
    <option value="2">Communication</option>
    <option value="3">Communication</option>
</select>

Wow, no really reusable solutions among answers yet.. I mean, a standart event handler should get only an event argument and doesn't have to use ids at all.. I'd use:

function handleSelectChange(event) {

    // if you want to support some really old IEs, add
    // event = event || window.event;

    var selectElement = event.target;

    var value = selectElement.value;
    // to support really old browsers, you may use
    // selectElement.value || selectElement.options[selectElement.selectedIndex].value;
    // like el Dude has suggested

    // do whatever you want with value
}

You may use this handler with each – inline js:

<select onchange="handleSelectChange(event)">
    <option value="1">one</option>
    <option value="2">two</option>
</select>

jQuery:

jQuery('#select_id').on('change',handleSelectChange);

or vanilla JS handler setting:

var selector = document.getElementById("select_id");
selector.onchange = handleSelectChange;
// or
selector.addEventListener('change', handleSelectChange);

And don't have to rewrite this for each select element you have.

Example snippet:

function handleSelectChange(event) {

    var selectElement = event.target;
    var value = selectElement.value;
    alert(value);
}

<select onchange="handleSelectChange(event)">
    <option value="1">one</option>
    <option value="2">two</option>
</select>

No need for an onchange function. You can grab the value in one line:

document.getElementById("select_id").options[document.getElementById("select_id").selectedIndex].value;

Or, split it up for better readability:

var select_id = document.getElementById("select_id");

select_id.options[select_id.selectedIndex].value;

let dropdown = document.querySelector('select');
if (dropdown) dropdown.addEventListener('change', function(event) {
    console.log(event.target.value);
});

HTML:

<select onchange="cityChanged(this.value)">
      <option value="CHICAGO">Chicago</option>
      <option value="NEWYORK">New York</option>
</select>

JS:

function cityChanged(city) {
    alert(city);
}