jQuery变量总是计算为'undefined'

Question

我正在尝试这样的事情:

var usernameDone = false;
/*Some application logic*/
alert(usernameDone);

这总是在评估undefined.但是,如果我将变量名称更改usernameDone为其他任何名称,即使usrnameDone脚本也能正常工作.是否usernameDone冲突与jQuery？如果没有,那为什么会发生？

(我目前正在使用jQuery-1.6.1在Chrome上进行测试,但尚未尝试其他浏览器.)

[更新]即使消除了应用程序逻辑
,变量undefined也会计算.

[更新-2完整代码]
我已使用//注释标记了用法

 $('document').ready( function() {

/**
 * The following set manages the effects for the login menu. The effects including highlighting
 * the login box when focused, showing guidance through a pop-up menu and handling transformation
 * through fade effects.
 * 
 */
var usernameDone = false;      //Declared here
/**
 * @function login-box focus()
 * Handles the onFocus() effects of the login box and displays the initial guidance pop-up box.
 * 
 */

$('#login-box').focus( function() {

/**
 * Color change effect of the login box
 */

    $(this).css('background-color' , '#000');
    $(this).css('color' , '#FFF');
    $(this).css('border' , '2px solid #000');

/**
 * Fade in effect of the login guide
 */

    $('#login-guide').fadeIn(1200);
    $('#login-guide-triangle').fadeIn(1200);

});


/**
 * @function login-box focusout()
 * Handles the focusOut effects of the login box and hides the guidance pop-up box.
 * 
 */

$('#login-box').focusout( function() {

/**
 * Color change effects of the login box
 */

    $(this).css('background-color' , '#FFF');
    $(this).css('color' , '#000');
    $(this).css('border' , '3px solid #000');

/**
 * Fade out effect of the login guide
 */

    $('#login-guide').fadeOut(1200);
    $('#login-guide-triangle').fadeOut(1200);
});

/**
 * @function login-box bind(keypress)
 * Handles the progression of the login steps. Specifically, what state the login box is in 
 * (ie, username or password) and how to respond when the state change key ('return/enter key')
 * is pressed.
 * 
 */

$('#login-box').bind('keypress' , function(e) {
/**
 * Checks for the current state (using usernameDone) if not, then registers the current username
 * changes the state to username done and converts the login box into password. Also, changes the
 * guidance contents.
 */
    alert(usernameDone);    //Always undefined (no modification before this)
    if(e.keyCode == 13 && usernameDone == false) {    //Owing to undefined it never evaluates to true.
        var loginUsername = $(this).val();
        $(this).val('');
        var usernameDone = true;
        $(this).fadeOut(0);
        document.getElementById('login-box').setAttribute('type' , 'password');
        $('#login-guide-title').html('Password');
        $('#login-guide-info').html('Press enter to login');
        $(this).fadeIn(800);
    }
});

});

Answer 1

当然会是这样undefined,因为你ready在字符串'document'上监听不在变量上的事件document.不要document用单引号或双引号括起变量,否则ready事件永远不会触发,因此永远不会定义变量.另外,不要再声明变量usernameDone有var usernameDone = true;,只是分配这样一个值给它usernameDone = true;,因为它已被定义.