Unexpected alert being called_问答_开发者_运维开发者技术经验分享

开发者 https://www.devze.com 2023-03-02 17:19 出处：网络

I have the following simple script on a page <!DOCTYPE html PUBLIC \"-//W3C//DTD XHTML 1.0 Transitional//EN\" \"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd\">

相关专题：javascript

I have the following simple script on a page

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" >
<head>
    <title>Untitled Page</title>
    <script type="text/javascript">
        var nsTest = function ()
        {
            var test = function ()
            {
                alert('nsTest.test');
            }

            var test2 = function ()
            {
                alert('nsTest.test2');
            }

            return {
                test: test,
                test2: test2
            }
        } ();

        function t()
        {
            alert(nsTest.test());
        }

        function t2()
        {
            alert(nsTest.test2());
        }
    </script>
</head>
<body>
    <input type="button" value="test" onclick="t()" />
    <开发者_如何学JAVA;input type="button" value="test2" onclick="t2()" />
</body>
</html>

When I click on either of the buttons I see the expected alert on the screent and then a second alert that says 'undefined'.

This is happening in IE8 and FF3. Any ideas what is going on?

Thanks,

David

Your saying alert twice. You do not need to say

alert(nsTest.test2());

you just need to call nsTest.test2();

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" >
<head>
    <title>Untitled Page</title>
    <script type="text/javascript">
        var nsTest = function ()
        {
            var test = function ()
            {
                alert('nsTest.test');
            }

            var test2 = function ()
            {
                alert('nsTest.test2');
            }

            return {
                test: test,
                test2: test2
            }
        }();

        function t()
        {
            nsTest.test();
        }

        function t2()
        {
            nsTest.test2();
        }
    </script>
</head>
<body>
    <input type="button" value="test" onclick="t()" />
    <input type="button" value="test2" onclick="t2()" />
</body>
</html>

Actually you do not even need a function t1 and t2 you can just have your onclick reference nsTest.test2() directly as shown here http://jsbin.com/ageva5/2/edit

You call t() which calls nsTest.test() …

nsTest.test() alerts the string 'nsTest.test' and then has no return value so returns undefined.

… t() then receives the return value and alerts it.

First the alerts in nsTest are run then the alerts in t() and t2() are run. These alerts alert the return value of nsTest.*. These value are undefined. Remove these alerts to only get the first alert.