When anchor part is changed, then the onhashchange event occurs. You can try to run the following code to learn how to implement onhashchange event in JavaScript.
Example
<!DOCTYPE html>
<html>
<body onhashchange="newFunc">
<button onclick="functionChange()">Click to change anchor</button>
<script>
function functionChange() {
location.hash = "about";
var hash = location.hash;
document.write("The anchor part is now: " + hash);
}
// If the achor part is changed
function newFunc() {
alert("Anchor part changed!");
}
</script>
</body>
</html>