html seleziona segnaposto
Placeholder attribute does not exist for the <select> tag.
But there are some ways to make a placeholder for the select box.
The easiest way of making a placeholder for the <select> element is using the disabled and selected attributes with the HTML5 hidden global attribute.
<select name="monthname" required>
<option value="" selected disabled hidden>Select Month</option>
<option value="Jan">January</option>
<option value="Feb">February</option>
<option value="Mar">March</option>
<option value="Apr">April</option>
<option value="May">May</option>
<option value="Jun">June</option>
<option value="Jul">July</option>
<option value="Aug">August</option>
<option value="Sep">September</option>
<option value="Oct">October</option>
<option value="Nov">November</option>
<option value="Dec">December</option>
</select>
js selezionare il valore di modifica
document.getElementById('my-select').addEventListener('change', function() {
console.log('You selected: ', this.value);
});
casella di testo html js sul cambiamento
<!--
You can use any of the following:
onkeydown, onkeyup or onchange
-->
<input type="text" onkeydown="keydownFunction()"
onkeyup="keyupFunction()" onchange="changeFunction()">
onchange su seleziona tag
<select id="comboA" onchange="getComboA(this)">
<option value="">Select combo</option>
<option value="Value1">Text1</option>
<option value="Value2">Text2</option>
<option value="Value3">Text3</option>
</select>
seleziona modulo invia onchange
<select onchange="this.form.submit()">
...
</select>
ingresso javascript onchange ottenere valore
var element = document.getElementById("myInput");
element.onchange = function() {
console.log(element.value);
}