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<td WIDTH="77%" VALIGN="MIDDLE"><font FACE="宋體" LANG="ZH-CN" SIZE="4" COLOR="#ff0000"></font><b><font
FACE="System,黑體" LANG="ZH-CN" SIZE="5" COLOR="#ff0000">第</font><font FACE="宋體"
LANG="ZH-CN" SIZE="5" COLOR="#ff0000">9</font><font FACE="System,黑體" LANG="ZH-CN"
SIZE="5" COLOR="#ff0000">頁(yè)：選單</font></b><font FACE="System,黑體" LANG="ZH-CN"><br>
<!-- BYLINE --> </font><font FACE="System,黑體" LANG="ZH-CN" SIZE="2">作者：</font><a
HREF="mailto:thau@wired.com"><font FACE="宋體" LANG="ZH-CN" SIZE="2">Thau!</font></a><font
FACE="宋體" LANG="ZH-CN"> <!-- SEE ALSO LINKS --></font></td>
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<td WIDTH="77%" VALIGN="MIDDLE" BGCOLOR="#ffffff"><font FACE="System,黑體" LANG="ZH-CN">選單是我們所學(xué)的表單選項(xiàng)中最奇特的一種。有兩<br>
種基本的格式：下列選單和列表選單。以下為例<br>
子：<form>
<b><p>下列選單</font><font FACE="宋體" LANG="ZH-CN">:</b><br>
<select NAME="pulldown_1" size="1">
<option>probiscus </option>
<option>spider </option>
<option>lemur </option>
<option>chimp </option>
<option>gorilla </option>
<option>orangutan </option>
</select> </p>
</font><b><font FACE="System,黑體" LANG="ZH-CN"><p>列表選單</font><font
FACE="宋體" LANG="ZH-CN">:</b><br>
<select NAME="list_1" SIZE="3">
<option>probiscus </option>
<option>spider </option>
<option>lemur </option>
<option>chimp </option>
<option>gorilla </option>
<option>orangutan </option>
</select> </font></p>
</form>
<font FACE="System,黑體" LANG="ZH-CN"><p>它的奇特之處在于這個(gè)選單有名稱，但其中的各個(gè)<br>
選項(xiàng)沒(méi)有名稱。例如，在</font><font FACE="宋體" LANG="ZH-CN">HTML</font><font
FACE="System,黑體" LANG="ZH-CN">中，第</font><font FACE="宋體" LANG="ZH-CN">1</font><font
FACE="System,黑體" LANG="ZH-CN">個(gè)選單如<br>
下：</font> </td>
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<pre><big>
<select name="pulldown_1" size=1>
<option>probiscus
<option>spider
<option>lemur
<option>chimp
<option>gorilla
<option>orangutan
</select>
</big></pre>
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<td WIDTH="77%" VALIGN="MIDDLE" BGCOLOR="#ffffff"><font FACE="System,黑體" LANG="ZH-CN">注意這個(gè)選單的名稱是</font><tt>pulldown_1</tt><font
FACE="System,黑體" LANG="ZH-CN">，但各個(gè)選項(xiàng)沒(méi)<br>
有名稱。所以要調(diào)用其中的各個(gè)選項(xiàng)則有點(diǎn)困難。<p>幸好數(shù)組可以幫助我們調(diào)用其中的選項(xiàng)。如果你想<br>
改變?cè)撓铝羞x單中的第</font><font FACE="宋體" LANG="ZH-CN">2</font><font
FACE="System,黑體" LANG="ZH-CN">個(gè)選項(xiàng)，你可以這樣做：</font></td>
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<pre><big>
window.document.form_1.pulldown_1.options[1].text = 'new_text';
</big></pre>
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<td WIDTH="77%" VALIGN="MIDDLE" BGCOLOR="#ffffff"><font FACE="System,黑體" LANG="ZH-CN">這是因?yàn)檫x單的元素有一個(gè)選項(xiàng)屬性，而該屬性是<br>
選單所有選項(xiàng)的集合而成的數(shù)組。點(diǎn)擊</font><a HREF="#"><font FACE="宋體"
LANG="ZH-CN"><b>錯(cuò)誤！超級(jí)鏈接引用無(wú)效。</b></font></a><font
FACE="System,黑體" LANG="ZH-CN">然后從下拉選單從下列選單中查看其選項(xiàng)是<br>
否已經(jīng)被改變。現(xiàn)在第</font><font FACE="宋體" LANG="ZH-CN">2</font><font
FACE="System,黑體" LANG="ZH-CN">個(gè)選項(xiàng)應(yīng)該是</font><tt><font FACE="宋體"
LANG="ZH-CN">*thau*</font><font FACE="System,黑體" LANG="ZH-CN">。</tt><p>除了選項(xiàng)屬性，選單還有一項(xiàng)屬性叫做<br>
</font><tt>selectedIndex</tt><font FACE="System,黑體" LANG="ZH-CN">。大筆一個(gè)選項(xiàng)被選擇后，<br>
</font><tt>selectedIndex</tt><font FACE="System,黑體" LANG="ZH-CN">屬性將變成被選項(xiàng)的數(shù)組索引號(hào)<br>
（序列號(hào)）。選擇第</font><font FACE="宋體" LANG="ZH-CN">2</font><font
FACE="System,黑體" LANG="ZH-CN">個(gè)列表選單中的一個(gè)選項(xiàng)，<br>
FACE="宋體" LANG="ZH-CN">1</font><font FACE="System,黑體" LANG="ZH-CN">個(gè)選項(xiàng)的索引<br>
號(hào)是</font><font FACE="宋體" LANG="ZH-CN">0</font><font FACE="System,黑體"
LANG="ZH-CN">。</font></td>
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<pre><big><a href="#" onClick="alert('index is: ' +
window.document.form_1.list_1.selectedIndex);
return false;">check the index.</a>
</big></pre>
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<td WIDTH="77%" VALIGN="MIDDLE" BGCOLOR="#ffffff"><font FACE="System,黑體" LANG="ZH-CN">表單的名稱是</font><tt>form_1</tt><font
FACE="System,黑體" LANG="ZH-CN">，列表選單的名稱是</font><tt>list_1</tt><font
FACE="System,黑體" LANG="ZH-CN">。</font><font FACE="宋體" LANG="ZH-CN"> </font><font
FACE="System,黑體" LANG="ZH-CN"><br>
</font><tt>selectedIndex</tt><font FACE="System,黑體" LANG="ZH-CN">屬性值為<br>
</font><tt>window.document.form_1.list_1.selectedIndex</tt><font FACE="System,黑體"
LANG="ZH-CN">。<br>
你還可以將</font><tt>selectedIndex</tt><font FACE="System,黑體" LANG="ZH-CN">設(shè)置如下：</font></td>
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<pre><big>window.document.form_1.list_1.selectedIndex = 1;
</big></pre>
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<td WIDTH="77%" VALIGN="MIDDLE" BGCOLOR="#ffffff"><font FACE="System,黑體" LANG="ZH-CN">并高亮度顯示第</font><font
FACE="宋體" LANG="ZH-CN">2</font><font FACE="System,黑體" LANG="ZH-CN">個(gè)選項(xiàng)。<br>
<br>
一旦你得到被選項(xiàng)的索引號(hào)，你就可以發(fā)現(xiàn)其內(nèi)<br>
容：</font> </td>
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<td WIDTH="77%" VALIGN="TOP" BGCOLOR="#ffffff"><dir>
<pre><big>
var the_select = </big>
<big>window.document.form_1.list_1;
var the_index = </big>
<big>the_select.selectedIndex;
var the_selected = </big>
<big>the_select.options[the_index].text;
</big></pre>
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<td WIDTH="77%" VALIGN="MIDDLE" BGCOLOR="#ffffff"><font FACE="System,黑體" LANG="ZH-CN"></font><tt>selectedIndex</tt><font
FACE="System,黑體" LANG="ZH-CN">屬性很有用，但如果有多個(gè)選項(xiàng)同時(shí)<br>
被選中，會(huì)如何呢？有關(guān)這方面的內(nèi)容請(qǐng)閱讀<br>
</font><a HREF="tppmsgs/msgs1.htm#100"><font FACE="宋體" LANG="ZH-CN">multiple selects</font></a><font
FACE="System,黑體" LANG="ZH-CN">。<p>選單元素的處理器為</font><tt>onChange()</tt><font
FACE="System,黑體" LANG="ZH-CN">。當(dāng)選單發(fā)生變化<br>
時(shí)，則該處理器被激活。</font></td>
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<td WIDTH="77%" VALIGN="TOP" BGCOLOR="#ffffff"><big><!-- PAGE X LINKS --></big><!-- this stuff checks if there are more pages in this story. if so, we'll
suck out the titles of those pages and build links. Right now, the maximum is
15 pages. --><!-- this is a mini-template that formats each pageX link. So, if a story
has 15 pages, we need to generate 15 links to it. This is how each one
will look... --> <font FACE="System,黑體"
LANG="ZH-CN"><p>第</font><font FACE="宋體" LANG="ZH-CN">1</font><font
FACE="System,黑體" LANG="ZH-CN">頁(yè)：<a HREF="tutorial5_page1.htm">第</font><font
FACE="宋體" LANG="ZH-CN">5</font><font FACE="System,黑體" LANG="ZH-CN">日課程介紹</a><br>
第</font><font FACE="宋體" LANG="ZH-CN">2</font><font FACE="System,黑體" LANG="ZH-CN">頁(yè)：<a
HREF="tutorial5_page2.htm">介紹反饋表單</a><br>
第</font><font FACE="宋體" LANG="ZH-CN">3</font><font FACE="System,黑體" LANG="ZH-CN">頁(yè)：<a
HREF="tutorial5_page3.htm">控制文字域的值</a><br>
第</font><font FACE="宋體" LANG="ZH-CN">4</font><font FACE="System,黑體" LANG="ZH-CN">頁(yè)：<a
HREF="tutorial5_page4.htm">文字域事件</a><br>
第</font><font FACE="宋體" LANG="ZH-CN">5</font><font FACE="System,黑體" LANG="ZH-CN">頁(yè)：<a
HREF="tutorial5_page5.htm">反饋表單處理器</a><br>
第</font><font FACE="宋體" LANG="ZH-CN">6</font><font FACE="System,黑體" LANG="ZH-CN">頁(yè)：<a
HREF="tutorial5_page6.htm">文字域的練習(xí)</a><br>
第</font><font FACE="宋體" LANG="ZH-CN">7</font><font FACE="System,黑體" LANG="ZH-CN">頁(yè)：<a
HREF="tutorial5_page7.htm">復(fù)選框</a><br>
第</font><font FACE="宋體" LANG="ZH-CN">8</font><font FACE="System,黑體" LANG="ZH-CN">頁(yè)：<a
HREF="tutorial5_page8.htm">單選框</a><br>
第</font><font FACE="宋體" LANG="ZH-CN">9</font><font FACE="System,黑體" LANG="ZH-CN">頁(yè)：<a
HREF="tutorial5_page9.htm">選單</a><br>
第</font><font FACE="宋體" LANG="ZH-CN">10</font><font FACE="System,黑體"
LANG="ZH-CN">頁(yè)：<a HREF="tutorial5_page10.htm">在選單中應(yīng)用</font><font
FACE="宋體" LANG="ZH-CN">onchange</font><font FACE="System,黑體" LANG="ZH-CN">命令</a><br>
</p>
</font><font FACE="System,黑體" LANG="ZH-CN" SIZE="2"><p> </p>
</font><font FACE="System,黑體" LANG="ZH-CN" SIZE="4"><p><br>
</p>
</font><font FACE="System,黑體" LANG="ZH-CN" SIZE="2"><p><br>
<!-- AUTHOR TAGLINE --> </font></td>
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<p> </p>
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