4.htm

javascript book

      <p style="text-indent: -18pt; tab-stops: list 72.0pt; mso-list: l7 level2 lfo2; line-height: 150%; margin-left: 72pt"><span lang="EN-US" style="FONT-FAMILY: 'Courier New'; FONT-SIZE: 10pt; mso-bidi-font-size: 12.0pt; mso-bidi-font-family: 'Times New Roman'"><font size="3">o<span style="FONT: 7pt 'Times New Roman'">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;  
      </span></font></span><font size="3"><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">该语句的优点就是无需知道对象中属性的个数即可进行操作。</span></font></p> 
      <p style="line-height: 150%; margin-left: 72pt"><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'"><font size="3">例：下列函数是显示数组中的内容：</font></span></p> 
      <p style="line-height: 150%; margin-left: 72pt"><span lang="EN-US"><font size="3">Function   
      showData(object)</font></span></p>  
      <p style="line-height: 150%; margin-left: 72pt"><span lang="EN-US"><font size="3">for   
      (var X=0; X&lt;30;X++)</font></span></p>  
      <p style="line-height: 150%; margin-left: 72pt"><font size="3"><span lang="EN-US">document.write(object[i])</span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">；</span></font></p> 
      <p style="line-height: 150%; margin-left: 72pt"><font size="3"><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">该函数是通过数组下标顺序值，来访问每个对象的属性，使用这种方式首先必须知道数组的下标值，否则若超出范围，则就会发生错误。而使</span><span lang="EN-US">For...in</span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">语句，则根本不需要知道对象属性的个数，见下：</span></font></p> 
      <p style="line-height: 150%; margin-left: 72pt"><span lang="EN-US"><font size="3">Function   
      showData(object)</font></span></p>  
      <p style="line-height: 150%; margin-left: 72pt"><span lang="EN-US"><font size="3">for(var   
      prop in object)</font></span></p>  
      <p style="line-height: 150%; margin-left: 72pt"><font size="3"><span lang="EN-US">document.write(object[prop])</span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">；</span></font></p> 
      <p style="line-height: 150%; margin-left: 72pt"><font size="3"><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">使用该函数时，在循环体中，</span><span lang="EN-US">For</span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">自动将的属性取出来，直到最后为此。</span></font></p> 
      <p style="text-indent: -18pt; tab-stops: list 36.0pt; mso-list: l1 level1 lfo3; line-height: 150%; margin-left: 36pt"><span lang="EN-US"><font size="3">2.<span style="FONT: 7pt 'Times New Roman'">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;  
      </span></font></span><font size="3"><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">、</span><span lang="EN-US">with</span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">语句</span></font></p> 
      <p style="line-height: 150%; margin-left: 36pt"><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'"><font size="3">使用该语句的意思是：在该语句体内，任何对变量的引用被认为是这个对象的属性，以节省一些代码。</font></span></p> 
      <p style="line-height: 150%; margin-left: 36pt"><span lang="EN-US"><font size="3">with   
      object{</font></span></p>  
      <p style="line-height: 150%; margin-left: 36pt"><span lang="EN-US"><font size="3">...}</font></span></p> 
      <p style="line-height: 150%; margin-left: 36pt"><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'"><font size="3">所有在</font></span><font size="3"><span lang="EN-US">with</span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">语句后的花括号中的语句，都是在后面</span><span lang="EN-US">object</span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">对象的作用域的。</span></font></p> 
      <p style="text-indent: -18pt; tab-stops: list 36.0pt; mso-list: l1 level1 lfo3; line-height: 150%; margin-left: 36pt"><span lang="EN-US"><font size="3">3.<span style="FONT: 7pt 'Times New Roman'">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;  
      </span></font></span><font size="3"><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">、</span><span lang="EN-US">this</span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">关键字</span></font></p> 
      <p style="line-height: 150%; margin-left: 36pt"><span lang="EN-US"><font size="3">this</font></span><font size="3"><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">是对当前的引用，在</span><span lang="EN-US">JavaScript</span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">由于对象的引用是多层次，多方位的，往往一个对象的引用又需要对另一个对象的引用，而另一个对象有可能又要引用另一个对象，这样有可能造成混乱，最后自己已不知道现在引用的那一个对象，为此</span><span lang="EN-US">JavaScript</span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">提供了一个用于将对象指定当前对象的语句</span><span lang="EN-US">this</span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">。</span></font></p> 
      <p style="text-indent: -18pt; tab-stops: list 36.0pt; mso-list: l1 level1 lfo3; line-height: 150%; margin-left: 36pt"><span lang="EN-US"><font size="3">4.<span style="FONT: 7pt 'Times New Roman'">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;  
      </span></font></span><font size="3"><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">、</span><span lang="EN-US">New</span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">运算符</span></font></p> 
      <p style="line-height: 150%; margin-left: 72pt"><font size="3"><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">虽然在</span><span lang="EN-US">JavaScript</span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">中对象的功能已经是非常强大的了。但更强大的是设计人员可以按照需求来创建自己的对象，以满足某一特定的要求。使用</span><span lang="EN-US">New</span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">运算符可以创建一个新的对象。其创建对象使用如下格式：</span></font></p> 
      <p style="line-height: 150%; margin-left: 72pt"><span lang="EN-US"><font size="3">Newobject=NEW   
      Object(Parameters table);</font></span></p>  
      <p style="line-height: 150%; margin-left: 72pt"><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'"><font size="3">其中</font></span><font size="3"><span lang="EN-US">Newobject</span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">创建的新对象：</span><span lang="EN-US">object</span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">是已经存在的对象；</span><span lang="EN-US">  
      parameters table</span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">参数表；</span><span lang="EN-US">new</span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">是</span><span lang="EN-US">JavaScript</span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">中的命令语句。</span></font></p>  
      <p style="line-height: 150%; margin-left: 72pt"><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'"><font size="3">如创建一个日期新对象</font></span></p> 
      <p style="line-height: 150%; margin-left: 72pt"><span lang="EN-US"><font size="3">newData=New   
      Data()</font></span></p>  
      <p style="line-height: 150%; margin-left: 72pt"><span lang="EN-US"><font size="3">birthday=New   
      Data (December 12.1998)</font></span></p>  
      <p style="line-height: 150%; margin-left: 72pt"><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'"><font size="3">之后就可使</font></span><font size="3"><span lang="EN-US">NewData</span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">、</span><span lang="EN-US">birthday</span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">作为一个新的日期对象了。</span></font></p> 
      <p style="line-height: 150%"><b><font size="3"><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">　</span><span lang="EN-US"><o:p> 
      </o:p> 
      </span></font></b></p> 
      <p style="line-height: 150%"><b><font size="3"><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">４、对象属性的引用</span>  
      <span lang="EN-US"><o:p>  
      </o:p>  
      </span></font></b></p>  
      <p style="line-height: 150%"><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'"><font size="3">　　对象属性的引用可由下列三种方式之一实现：</font></span></p> 
      <p style="line-height: 150%"><font size="3"><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">（１）使用点（</span><span lang="EN-US">.</span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">）运算符</span></font></p> 
      <p style="line-height: 150%"><span lang="EN-US"><font size="3">university.Name=“</font></span><font size="3"><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">云南省</span><span lang="EN-US">”</span></font></p> 
      <p style="line-height: 150%"><font size="3"><span lang="EN-US">university.city=“</span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">昆明市</span><span lang="EN-US">”</span></font></p> 
      <p style="line-height: 150%"><span lang="EN-US"><font size="3">university.Date=&quot;1999&quot;</font></span></p>