``` <input type="button" value="点击" id="btn"> <img src="images/logo_03.png" alt="" id="img"> <script> var btn = document.getElementById('btn'); var flag = 1; btn.onclick = function () { var img = document.getElementById('img'); if (flag === 1){ img.src = 'images/banner_03.png'; flag = 2; }else{ img.src = 'images/logo_03.png'; flag = 1; } } </script> ```