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<!DOCTYPE html> <html> <body> <p>This example uses the HTML DOM to assign an "onfocusin" event to an input element.</p> Enter your name: <input type="text" id="fname"> <p><strong>Note:</strong> Firefox does not support the onfocusin event.</p> <p><strong>Note:</strong> This example may not work as expected in Chrome, Safari and Opera 15+.</p> <script> document.getElementById("fname").onfocusin = function() {myFunction()}; function myFunction() { document.getElementById("fname").style.backgroundColor = "red"; } </script> </body> </html>