​x
 
<!DOCTYPE html>
<html>
<body>
​
<p>按住文本字段内的某个键可设置红色背景色。松开按键可设置绿色背景色。</p>
​
<input type="text" id="demo" onkeydown="keydownFunction()" onkeyup="keyupFunction()">
​
<script>
function keydownFunction() {
  document.getElementById("demo").style.backgroundColor = "red";
}
​
function keyupFunction() {
  document.getElementById("demo").style.backgroundColor = "green";
}
</script>
​
</body>
</html>
​