<!DOCTYPE html>
<html>
<body>
<p>When you enter the input field (child of FORM), a function is triggered which sets the background color to yellow. When you leave the input field, a function is triggered which removes the background color.</p>
<form id="myForm">
<input type="text" id="myInput">
</form>
<p><strong>Note:</strong> Firefox does not support the focusin and focusout events.</p>
<script>
var x = document.getElementById("myForm");
x.addEventListener("focusin", myFocusFunction);
x.addEventListener("focusout", myBlurFunction);
function myFocusFunction() {
document.getElementById("myInput").style.backgroundColor = "yellow";
}
function myBlurFunction() {
document.getElementById("myInput").style.backgroundColor = "";
}
</script>
</body>
</html>