console 命令行工具 X clear

console

function showMessage1(){
  document.write("You have clicked the button!");
}
  var btn1 = document.getElementById('btn1');
  btn1.onclick = function(){
    document.write('BTN1');
  }
  var btn2 = document.getElementById('btn2');
	btn2.addEventListener('click',function(){
    document.write('BTN2')
  },false)

<!DOCTYPE html>

<html lang="en">

<head>

  <meta charset="UTF-8" />

  <title>事件处理程序</title>

</head>

<body>
<h4>HTML事件处理程序</h4>
  <input type="button" onclick="try{showMessage1();}catch(ex){}" />
<h4>DOM0级事件处理程序</h4>
  <input type="button" id='btn1' />
<h4>DOM2级事件处理程序</h4>
  <input type="button" id='btn2' />
</body>

</html>