JavaScript -- throw、try 和 catch

<!DOCTYPE html>
<html>

    <head>
        <meta charset="utf-8">
        <title>JavaScript异常处理</title>
    </head>

    <body>

        <p>请输出一个 5 到 10 之间的数字:</p>

        <input id="demo" type="text">
        <button type="button" onclick="exception()">测试输入</button>
        <p id="message"></p>
        <script type="text/javascript" src="test.js"></script>
    </body>

</html>

function exception() {
    var message, x;
    message = document.getElementById("message");
    message.innerHTML = "";
    x = document.getElementById("demo").value;
    try { 
        if(x == "")  throw "值为空";
        if(isNaN(x)) throw "不是数字";
        x = Number(x);
        if(x < 5)    throw "太小";
        if(x > 10)   throw "太大";
        if(x>5 && x<10){
            message.innerHTML = "正确: " + x;
        }
    }
    catch(err) {
        message.innerHTML = "错误: " + err;
    }
}