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<td bgcolor="#ffff99" width="451">JavaScript高级教程 - 第四课</td>
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<td bgcolor="#FF6600" width="451"><a href="mailto:thau@wired.com">Thau</a></td>
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<td width="591" valign="top" align="left" rowspan="2"><small><small><br>
</small></small><strong>第十页：<font size="3">另一种获取难以索引的对象的手段</font></strong>
<p><font size="3"> </font></p>
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<td width="445"> <font face="helvetica, arial, sans-serif" size="2"></font><font size="3">这就是我们迄今为止学到的获取图象对象的手段：</font></td>
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<pre><font face="verdana, arial" size="2">function simpleSwap()
{
var the_image = prompt("change parrot or cheese","");
var the_image_name = "window.document." + the_image;
var the_image_object = eval(the_image_name);
the_image_object.src = "ant.gif";
}</font><font face="verdana, arial" size="1">
</font></pre>
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<td width="444"> <font face="helvetica, arial, sans-serif" size="3"></font><font size="3">从这里延伸一下，你也可以通过图象的名字在图象关联数组<br>
中引用图象，比如：<tt><font face="verdana, arial">window.document.images<br>
["parrot"].src</font></tt></font><font size="3" face="verdana, arial">.
</font><font size="3">这就象通过数组的下标引用图象一样，如<br>
<font face="verdana, arial"><tt>window.document.images[0].src</tt>.
</font>所以，上面的代码可<br>
以重新写成：</font></td>
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<pre><font face="verdana, arial" size="2">function simpleSwap()
{
var the_image = prompt("change parrot or cheese","");
window.document.images[the_image].src = "ant.gif";
}</font></pre>
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<td width="440"> <font face="helvetica, arial, sans-serif" size="3"></font><font size="3">你可以用这种技巧获得你的各种对象。如果在一个表单里有<br>
一个文本框，象这样：
<blockquote>
<pre>
<font face="verdana, arial"></font>
<font face="verdana, arial"><form name="the_form">
<input type="text" name="the_text_box">
</form>
</font></pre>
</blockquote>
</font>
<p><font size="3"> <font face="verdana, arial"></font>你可以用这个来改变文本框里的文本：</font></p>
<p>window.document.forms["the_form"].elements["the_text_box"].value
= "hello!";</p>
<p><font size="3">现在你已经知道了好几种获取和改变对象信息的途径了。在<br>
上面的例子里，我们可以用四种手段来设置文本框的文本：</font>
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<blockquote>
<pre><big>
</big>var the_form_name = "the_form";
var the_element_name = "the_text_box";
</pre>
</blockquote>
<ol>
<li>window.document.forms[0].elements[0].value = "hello!";
</li>
<li>window.document.forms[the_form_name].elements[the_element_name].value
= "hello!"; </li>
<li>window.document.the_form.the_text_box.value = "hello!";
</li>
<li>var the_element_string = "window.document." + the_form_name
+ "." + the_element_name; var the_element = eval(the_element_string);
the_element_string.value = "hello!"; </li>
</ol>
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<td width="441"><font size="3">具体到你用哪个方法也许取决于你的心情以及你能想起来用<br>
那一个。
<p><font face="verdana, arial"></font>这就是我们今天的课程，我们来复习一下。<a href="day4_11.html">>></a>
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<p align="left"><font face="宋体" size="3" color="#000000"><strong>JavaScript高级教程</strong></font><font color="#FF0000" face="宋体" size="3"><br>
</font><font size="3"><font color="#FF3300">第一页</font> <a href="day4_1.html"><font face="verdana, arial, geneva, sans-serif">JavaScript</font>高级教程<font face="verdana, arial, geneva, sans-serif">-
</font>第<font face="verdana, arial, geneva, sans-serif">4</font>天</a>
<br>
<font color="#FF3300">第二页 </font><a href="day4_2.html">图象映射与<font face="verdana, arial, geneva, sans-serif">JavaScript</font></a><font face="verdana, arial, geneva, sans-serif"><br>
</font><font color="#FF3300">第三页 </font><a href="day4_3.html">预装图象 -
是什么<font face="verdana, arial, geneva, sans-serif">?</font></a><font face="verdana, arial, geneva, sans-serif"><br>
</font><font color="#FF3300">第四页 </font><a href="day4_4.html">预装图象 -
怎么做?</a><font face="verdana, arial, geneva, sans-serif"><br>
</font><font color="#FF3300">第五页 </font><a href="day4_5.html">对象的优点</a><br>
<font color="#FF3300">第六页 </font><a href="day4_6.html">创建你自己的对象</a><br>
<font color="#FF3300">第七页 </font><a href="day4_7.html">你的面向对象的虚拟宠物</a><br>
<font color="#FF3300">第八页 </font><a href="day4_8.html">计算字符串</a><br>
<font color="#FF3300">第九页 </font><a href="day4_9.html">获取难以索引的对象</a><br>
<font color="#FF3300">第十页 </font>另一种获取难以索引的对象的手段<br>
<font color="#FF3300">第十一页 </font><a href="day4_11.html">第四天课程复习</a></font></p>
<p>[<a href="day1_1.html">第1课</a>][<a href="day2_1.html">第2课</a>][<a href="day3_1.html">第3课</a>][第4课][<a href="day5_1.html">第5课</a>]</p>
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