代码实例：
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>test</title>
</head>
<body>
<script>
function AD() {
var control=document.forms[0]['test'];
var Direction=control.selectionDirection;
alert(Direction);
}
</script>
<form>
<input type="test" name="test">
<input type="button" value="点击一下" onclick="AD()">
</form>
</body>
</html>
效果：
2017-09-02 23:56:57