📄 day4_8.html
字号:
<html><head><meta http-equiv="Content-Type" content="text/html; charset=gb2312-80"><style type="text/css"><!--a:link { color: blue; text-decoration: none}a:visited { color: purple; text-decoration: none}a:hover { color: #CC0033; text-decoration: underline}--></style><title>JavaScript高级教程</title><script language="JavaScript"><!-- hide me// timedAlert// this just calls a function timedAlert(){ var the_timeout = setTimeout("alertAndRedirect();", 3000);}function alertAndRedirect(){ alert('OK! Exhale!'); window.location.replace("day3_2.html");}// show me --></script></head><body topmargin="1" leftmargin="2"><table border="0" width="591" cellspacing="0"> <tr> <td bgcolor="#ffff99" width="451">JavaScript高级教程 - 第四课</td> </tr> <tr> <td bgcolor="#FF6600" width="451"><a href="mailto:thau@wired.com">Thau</a></td> </tr></table><div align="left"> <table border="0" width="630" cellspacing="0"> <tr> <td width="458" valign="top" align="left" rowspan="2"><small><small><br> </small></small><strong>第八页：<font size="3">计算字符串</font></strong> <p><font face="verdana, arial, geneva, sans-serif" size="2"></font><font size="2"> <script language="JavaScript"><!-- hide mefunction doSillyEval(){ var the_unevaled_answer = "2 + 3"; var the_evaled_answer = eval("2 + 3"); alert("the un-evaled answer is " + the_unevaled_answer + " and the evaled answer is " + the_evaled_answer);} // show me --></script> </font></p> <table width="447"> <tr> <td width="443"> <font face="verdana, arial, geneva, sans-serif" size="2"></font><font face="helvetica, arial, sans-serif" size="3">JavaScript</font><font size="3">有许多小窍门来使编程更加容易。其中之一就是<br> </font><font face="verdana, arial" size="3"><tt>eval()</tt></font><font size="3">函数，这个函数可以把一个字符串当作一个</font><font face="verdana, arial" size="3">JavaScript</font><br> <font size="3">表达式一样去执行它。实际上我在<a href="../course/day5_1.html">基础教程第五日</a>里曾讲过<br> 一点有关</font><font face="verdana, arial" size="3">eval</font><font size="3">函数，这里举个小例子重温一下：</font></td> </tr> </table> <blockquote> <pre><big></big>var the_unevaled_answer = "2 + 3";var the_evaled_answer = eval("2 + 3");alert("the un-evaled answer is " + the_unevaled_answer + " and the evaled answer is " + the_evaled_answer);</pre> </blockquote> <table width="449"> <tr> <td width="445"><font size="3">如果你</font><a href="#" onClick="doSillyEval(); return false;"><font size="3">运行这段</font><font face="verdana, arial" size="3">eval</font><font size="3">程序</font></a><font face="verdana, arial" size="3">, </font><font size="3">你将会看到在</font><font face="verdana, arial" size="3">JavaScript</font><font size="3">里字<br> 符串</font><font face="verdana, arial" size="3">"2 + 3"</font><font size="3">实际上被执行了。所以当你把</font><font face="verdana, arial" size="3"><tt>the_evaled_answer</tt></font><br> <font size="3">的值设成 </font><font face="verdana, arial" size="3"><tt>eval("2 + 3")</tt></font><font size="3">时</font><font face="verdana, arial" size="3">, JavaScript</font><font size="3">将会明白并把</font><font face="verdana, arial" size="3">2</font><font size="3">和</font><font face="verdana, arial" size="3">3</font><br> <font size="3">的和返回给</font><font face="verdana, arial" size="3"><tt>the_evaled_answer</tt></font><font size="3">。</font> <p><font face="verdana, arial" size="3"></font><font size="3">这个看起来似乎有点傻，其实可以做出很有趣的事。比如使<br> 用</font><font face="verdana, arial" size="3">eval</font><font size="3">你可以根据用户的输入直接创建函数。这可以使程序<br> 根据时间或用户输入的不同而使程序本身发生变化，通过举<br> 一反三，你可以获得惊人的效果。在实际中，</font><font face="verdana, arial" size="3">eval</font><font size="3">很少被<br> 用到，但也许你见过有人使用</font><font face="verdana, arial" size="3">eval</font><font size="3">来获取难以索引的对象。<a href="day4_9.html">>></a></font> </td> </tr> </table> <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>计算字符串<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><a href="day4_10.html">另一种获取难以索引的对象的手段</a><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> <hr align="left"> <!--webbot bot="Include" U-Include="../../copyright.html" TAG="BODY" startspan --> <p><font face="verdana, arial, geneva, sans-serif" size="2"><a href="http://phtshop.yeah.net" target="_top">本文根据 网猴 相关文章改编，版权归原作者所有。</a> </font><font color="#000000"><span class="smallfont"></span></font></p> <!--webbot bot="Include" endspan i-checksum="15926" --> </td> </tr> <tr> </tr> </table></div></body></html>⌨️ 快捷键说明
复制代码
Ctrl + C
搜索代码
Ctrl + F
全屏模式
F11
切换主题
Ctrl + Shift + D
显示快捷键
?
增大字号
Ctrl + =
减小字号
Ctrl + -