Edit in JSFiddle

var SimpleListModel = function (items) {
    var self = this;
    self.shouldShowMessage = ko.observable(true) //初始化可见
    self.switchVisibility = function () {
        self.shouldShowMessage(!self.shouldShowMessage());//每次点击按钮的时候，修改observbale的值
    };
    self.desc = ko.computed(function () {
        return self.shouldShowMessage() ? "点击隐藏" : "点击显示";
    });//按钮上的文本值
};

ko.applyBindings(new SimpleListModel(), document.getElementById("Demo2"));

<h1>演示 KnockOut js表达式充当绑定值功能</h1>
<hr />
<ul>
    <li  class="Point">
    2、<b  class="PointTitle">理解<span class="KeyWord">表达式值</span>绑定</b><br />
        <ul class="PointDesc">
            <li>可以使用任意javascript表达式表示bool值</li>
        </ul>
        <div  class="PointDemo" id="Demo2">
            <div data-bind="visible: shouldShowMessage()==true">
                这里绑定的是js表达式 shouldShowMessage()==true
            </div>
            <button data-bind="click:switchVisibility,text:desc"></button>
        </div>
        <!--下面写一些特殊的提示信息-->
        <div class="PSFrame">
        shouldShowMessage()==true只是个演示，实际上可以使用任意的表达式，比如xxx().length<6
        </div>
        <hr />
    </li>
</ul>
<hr />

/*Demo�ļ���ʽ*/
body
{
    background-color: #e3e5d4;
}
/*  ֪ʶ��    */
.Point
{
    margin: 20px,0,0,0;
}
/*  ֪ʶ�����    */
.PointTitle
{
    color:#0d8d0d;
}
/*  �ؼ���    */
.KeyWord
{
    color:Red;
}
/*  ֪ʶ������    */
.PointDesc
{
    font-family: Arial;
    font-size: 15px;
    color:#09acb8;
}
.PointDesc li
{
    margin: 10px,0,0,0;
}
/*  ֪ʶ��Demo���    */
.PointDemo
{
    border-style:double; 
    border-color:#dcd559;
    min-height:100px;
    font-family: Corbel;
    font-size: 20px;
    color: #00174f;
}
/*  ��Ҫ������ʾ����Ϣ���    */
.PSFrame
{
    border-style: dashed; 
    border-color:#78e6ef;
    font-family: Corbel;
    font-size: 20px;
    font-style:italic;
    color: #b86c00;
}
/*  ������ʾ    */
.error {
    color:Red;
    
}
/*  **********************************************************    */
/*��Ҫǿ������ʽ*/
.Notice
{
    font-weight: bold;
    font-family:Bodoni MT Black;
    color: #cd0707;
}

/*  **********************************************************    */
/*�������ʽ*/
input[type="text"]
{
    min-width:250px;
}
select
{
    min-width:400px;
}