Edit in JSFiddle

//////////////////////          演示一、二     //////////////////////////
//演示ko的computed方法的第二个参数
var testOutModel = {
    p1: '我来自外部对象'
};
function AppViewModel() {
    var self = this;

    self.firstName = ko.observable('Bob');
    self.lastName = ko.observable('Smith');
    //这是一个计算属性
    self.fullName = ko.computed(function () {
        return self.firstName() + " " + self.lastName() + '：' + this.p1;
    }, testOutModel);
}
var model = new AppViewModel();

ko.applyBindings(model, document.getElementById("Demo1")); 

<h1>演示 KnockOut Computed属性基本 功能</h1>
<hr />
<ul>

    <li  class="Point">
    1、<b  class="PointTitle">理解<span class="KeyWord">"computed"</span>属性的参数</b><br />
        <ul class="PointDesc">
            <li>第一个参数负责计算新的属性值</li>
            <li>第二个参数负责指定第一个函数的this指针对象（函数调用对象）</li>
           
        </ul>
        <div  class="PointDemo" id="Demo1">
        firstName:<input type="text" data-bind='value: firstName, valueUpdate: "afterkeydown"' /><br />
        lastName:<input type="text" data-bind='value: lastName,valueUpdate: "afterkeydown"' /><br />
        动态计算的 fullName:<span class="Notice" data-bind='text: fullName'></span>
        </div>
        <!--下面写一些特殊的提示信息-->
        <div class="PSFrame">
        注意demo中computed的第二个参数传递了一个外部对象，所以在computed的function中就可以使用this访问到这个对象了

        </div>
        <hr />
    </li>
</ul>
<hr />

body
{
    background-color: #e3e5d4;
}
.Point
{
    margin: 20px,0,0,0;
}

.PointTitle
{
    color:#0d8d0d;
}

.KeyWord
{
    color:Red;
}

.PointDesc
{
    font-family: Arial;
    font-size: 15px;
    color:#09acb8;
}
.PointDesc li
{
    margin: 10px,0,0,0;
}

.PointDemo
{
    border-style:double; 
    border-color:#dcd559;
    min-height:100px;
    font-family: Corbel;
    font-size: 20px;
    color: #00174f;
}

.PSFrame
{
    border-style: dashed; 
    border-color:#78e6ef;
    font-family: Corbel;
    font-size: 20px;
    font-style:italic;
    color: #b86c00;
}

.error {
    color:Red;
    
}
/*  **********************************************************    */

.Notice
{
    font-weight: bold;
    font-family:Bodoni MT Black;
    color: #cd0707;
}

/*  **********************************************************    */

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