function toggleText(button_id) { var el = document.getElementById(button_id); if (el.firstChild.data == "Lock") { el.firstChild.data = "Unlock"; } else { el.firstChild.data = "Lock"; } } //Or even more compact like this: function toggleText(button_id) { var text = document.getElementById(button_id).firstChild; text.data = text.data == "Lock" ? "Unlock" : "Lock"; }