Event delegation: using the focusin event:
When you enter the input field, 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.
<!DOCTYPE html> <html> <body> <form id="myForm"> <input type="text" id="myInput"> </form>/*from w ww.j a v a 2s. c om*/ <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>