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<td bgcolor="#ffff99" width="451">JavaScript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="458" valign="top" align="left"><strong><small><small><br>
</small></small><font face="宋体" size="3">第九页：</font><font SIZE="3">数组和循环</font></strong>
<p><font SIZE="3">数组是一项非常有用的东西，因为你可以循环调用数组中的各<br>
个元素执行某项功能。以下是循环显示一个<a
href="javascript:if(confirm('http://www.hotwired.com/webmonkey/98/04/files1a/slideshow.html \n\nThis file was not retrieved by Teleport Pro, because it is addressed on a domain or path outside the boundaries set for its Starting Address. \n\nDo you want to open it from the server?'))window.location='http://www.hotwired.com/webmonkey/98/04/files1a/slideshow.html'" tppabs="http://www.hotwired.com/webmonkey/98/04/files1a/slideshow.html" target="_blank"><font
face="宋体">URL</font>数组中的各个元素</a><br>
的例子。</font></p>
<font SIZE="3"><p>首先，要使该例子发挥作用，我们需要声明一些变量：</p>
</font><p><font face="宋体"><br>
var url_names = new
Array("hits.org","awaken.org","bianca.com");<br>
<br>
var a_url;<br>
<big><br>
</big>接下来，我们循环调用数组中的各个元素，打开每<small><br>
</small>个URL并对待用户点击alert框的OK按钮：</font></p>
<p><font face="宋体"><br>
for (loop = 0; loop <url_names.length; loop++)<br>
<br>
{<br>
<br>
// make the name of a url, for example http://www.hits.org/<br>
<br>
a_url = "http://www." + url_names[loop] + "/";<br>
<br>
// open a window<br>
<br>
var new_window=open(a_url,"new_window","width=300,height=300");<br>
<br>
// wait for the click<br>
<br>
alert("hit ok for the next site"); <br>
<br>
}<br>
<br>
</font></p>
<p><font SIZE="3">首先，你会注意到循环从<font face="宋体">0</font>一直到<font
face="宋体"><tt>url_names.length</tt></font>这个变量。<br>
将<font face="宋体"><tt>.length</tt></font>放在数组名的后面由于告诉你数组中有多少个元素。<br>
但是，注意数组元素的数目同数组最后一个元素的索引号（顺<br>
序号）不同。如果数组中有<font face="宋体">3</font>个元素，则数组的长度为<font
face="宋体">3</font>，但是<br>
数组中最后一个元素的索引号却是<font face="宋体"><tt>array[2]</tt>.</font>。这是因为数组中<br>
第<font face="宋体">1</font>个元素的索引号是<font face="宋体"><tt>array[0]</tt>.</font>。如果你执行数组调用时得到<br>
诸如<font face="宋体">"object not found" </font>的错误信息，而你的代码中有一个<br>
数组，则有可能是因为你将数组元素的索引号同数组中元素的<br>
数目混淆了。</font></p>
<font SIZE="3"><p>不也许还会注意到将<font face="宋体"><tt>.length</tt></font>放在数组的结尾处很有点想给一个<br>
对象附加一些属性。这是因为数组本身就是对象，而<font face="宋体">length</font>就<br>
是数组的一项属性。</p>
<p>数组术语对象的另一个表现是：你需要用新指令才能生成新的<br>
数组。在上例中，<font face="宋体"><tt>url_names = new Array(......)</tt> </font>实际可以<br>
解释为：生成一个新数组，用<font face="宋体"><tt>url_names</tt></font>对其做一个引用。你可<br>
以注意到单词<font face="宋体">"new" </font>以这种方式被应用时，就生成了一个新的<br>
对象。</p>
<p>循环中的第<font face="宋体">1</font>行生成一个变量。其赋值为一个字符串。</p>
</font><p><font face="宋体">a_url = "http://www." + url_names[loop] +
"/";<br>
<br>
</font></p>
<p><font SIZE="3">循环开始时，变量循环的初始值为<font face="宋体">0</font>。<font
face="宋体"><tt>url_names</tt></font>数组的第<font face="宋体">1</font>个元<br>
素是字符串<font face="宋体"><tt>"hits.org"</tt>.</font>，所以在第一次循环中，变量<font
face="宋体"><tt>a_url</tt></font>等<br>
值于字符串<font face="宋体"><tt>"http://www.hits.org/"</tt>.</font>。</font></p>
<font SIZE="3"><p>循环的下一行用该<font face="宋体">URL</font>打开一个窗口
</p>
</font><p><font face="宋体">var
new_window=open(a_url,"new_window","width=300,height=300");<br>
<big><br>
</big></font></p>
<p><font SIZE="3">由于每次打开窗口时我们给窗口起的名称都一样，所以在转到<br>
新的<font face="宋体">URL</font>时，不会打开许多窗口。如果我们在上例中去掉窗口<br>
名称<font face="宋体"><tt>"new_window"</tt></font>，则每次循环时就会打开一个新窗口。
</font></p>
<font SIZE="3"><p>循环的第<font face="宋体">3</font>行只是打开一个<font
face="宋体">alert</font>框，并对待用户点击<font face="宋体">OK </font>按钮。
</p>
<p>数组还可以由于其它元素，而不只是字符串。数组可以应用<br>
于<font face="宋体">JavaScript</font>文件对象模块（<font face="宋体">Document
Object Model</font>）的各个<br>
方面。<a href="day4_10.html" tppabs="http://www.pchome.net/ch/tur/pstext/teacher/javascript/day4_10.html">>></a></p>
</font><p align="left"><font face="宋体" size="3" color="#000000"><strong>JavaScript教程</strong></font><font
color="#FF0000" face="宋体" size="3"><br>
</font><font size="3" color="#FF0000">第一页</font><font size="2" face="宋体"> </font><a
href="day4_9.html" tppabs="http://www.pchome.net/ch/tur/pstext/teacher/javascript/day4_9.html"><font SIZE="3">第四课介绍</font></a><font size="2"><br>
</font><font SIZE="3"><font color="#FF0000">第二页</font> <a href="day4_2.html" tppabs="http://www.pchome.net/ch/tur/pstext/teacher/javascript/day4_2.html">循环介绍</a></font><font
size="2"><br>
</font><font SIZE="3"><font color="#FF0000">第三页</font> <a href="day4_3.html" tppabs="http://www.pchome.net/ch/tur/pstext/teacher/javascript/day4_3.html">循环的密码</a></font><font
size="2"><br>
</font><font SIZE="3"><font color="#FF0000">第四页</font> <a href="day4_4.html" tppabs="http://www.pchome.net/ch/tur/pstext/teacher/javascript/day4_4.html">再谈<font
face="宋体">WHILE</font>循环</a></font><font size="2"><br>
</font><font SIZE="3"><font color="#FF0000">第五页</font> <a href="day4_5.html" tppabs="http://www.pchome.net/ch/tur/pstext/teacher/javascript/day4_5.html">For循环</a></font><font
size="2"><br>
</font><font SIZE="3"><font color="#FF0000">第六页</font> <a href="day4_6.html" tppabs="http://www.pchome.net/ch/tur/pstext/teacher/javascript/day4_6.html">嵌套循环</a></font><font
size="2"><br>
</font><font SIZE="3"><font color="#FF0000">第七页</font> <a href="day4_7.html" tppabs="http://www.pchome.net/ch/tur/pstext/teacher/javascript/day4_7.html">循环练习</a></font><font
size="2"><br>
</font><font SIZE="3"><font color="#FF0000">第八页</font> <a href="day4_8.html" tppabs="http://www.pchome.net/ch/tur/pstext/teacher/javascript/day4_8.html">数组</a></font><font
size="2"><br>
</font><font SIZE="3"><font color="#FF0000">第九页</font> 数组和循环</font><font
size="2"><br>
</font><font SIZE="3"><font color="#FF0000">第十页</font> <a href="day4_10.html" tppabs="http://www.pchome.net/ch/tur/pstext/teacher/javascript/day4_10.html">文件目标模块中的数组</a></font><font
size="2"><br>
</font><font SIZE="3"><font color="#FF0000">第十一页</font> <a href="day4_11.html" tppabs="http://www.pchome.net/ch/tur/pstext/teacher/javascript/day4_11.html">函数</a></font><font
size="2"><br>
</font><font SIZE="3"><font color="#FF0000">第十二页</font> <a href="day4_12.html" tppabs="http://www.pchome.net/ch/tur/pstext/teacher/javascript/day4_12.html">无参数函数</a></font><font
size="2"><br>
</font><font SIZE="3"><font color="#FF0000">第十三页</font> <a href="day4_13.html" tppabs="http://www.pchome.net/ch/tur/pstext/teacher/javascript/day4_13.html">参数及返回值</a></font><font
size="2"><br>
</font><font SIZE="3"><font color="#FF0000">第十四页</font> <a href="day4_14.html" tppabs="http://www.pchome.net/ch/tur/pstext/teacher/javascript/day4_14.html">多于一个参数的函数</a></font></p>
<p align="left"><font face="宋体" size="3">[<a href="index.html" tppabs="http://www.pchome.net/ch/tur/pstext/teacher/javascript/index.html">第1课</a>][<a
href="day2_1.html" tppabs="http://www.pchome.net/ch/tur/pstext/teacher/javascript/day2_1.html">第2课</a>][<a href="day3_1.html" tppabs="http://www.pchome.net/ch/tur/pstext/teacher/javascript/day3_1.html">第3课</a>][第4课][<a
href="day5_1.html" tppabs="http://www.pchome.net/ch/tur/pstext/teacher/javascript/day5_1.html">第5课</a>]</font></p>
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