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<title>JavaScrip高级教程</title>
<strong>第五页：<font face="宋体" size="3">变量的使用方法</font></strong>
<p>要使JavaScript中各种同名变量不会发生混淆，你可以在声明<br>
变量时在变量前面加上var。在一个函数内用var声明后灯的变<br>
量叫做局部变量，它只存在于该函数内部。通常情况下你应该<br>
尽量使用局部变量。</p>
<p>这里是用var声明后的正确的JavaScript代码：</p>
<p>function fahrenToCelsius(faren)<br>
<br>
{<br>
<br>
var temp = (faren - 32) * 5 / 9;<br>
return temp;<br>
}<br>
function convertTemp()<br>
{<br>
var temp = prompt("what temperature Fahrenheit?
","50");<br>
var celsius = badFahrenToCelsius(temp);<br>
alert(temp + " degrees Fahrenheit is " +
<br>
celsius + " degrees Celsius.");<br>
} <br>
<br>
现在当我们输入50时，<br>
<br>
<br>
(在convertTemp函数内部) temp = 50<br>
<br>
<br>
temp被传递到函数fahrenToCelsius()，在函数fahrenToCelsius<br>
()内部，参数faren现在被设定为50，然后temp 用以下代码<br>
设定：</p>
<p>var temp = (faren - 32) * 5 / 9;</p>
<p>由于这个temp变量前面用var做了声明，所以该变量筒其他函数<br>
中叫做temp的变量不同。执行完fahrenToCelsius()时，该函数<br>
种的temp即告消失。所以在fahrenToCelsius()返回数值前，</p>
<p>faren = 50<br>
<br>
(inside fahrenToCelsius) temp = 10<br>
<br>
(inside convertTemp) temp = 50<br>
<br>
fahrenToCelsius()然后返回它的变量temp值10。一旦我们<br>
从fahrenToCelsius()函数中出来，该函数中等temp变量的作用<br>
即告终止。当fahrenToCelsius() 返回时，它将变量的值设置<br>
为10: </p>
<p>(在convertTemp内部) temp = 50<br>
(在convertTemp内部) celsius = 10</p>
<p>现在显示的信息将是我们所希望的"50 degrees Fahrenheit is<br>
10 degrees Celsius"。</p>
<p><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 face="宋体" size="3"><font color="#FF0000">第一页</font> <a href="day1_5.html">Javascript高级教程</a><br>
<font color="#FF0000">第二页</font> <a href="day1_2.html">本教程的课程计划</a><br>
<font color="#FF0000">第三页</font> <a href="day1_3.html">一个if-then-else的快捷方式</a><br>
<font color="#FF0000">第四页</font> <a href="day1_4.html">什么是变量</a><br>
<font color="#FF0000">第五页</font> 变量的使用方法</font></p>
<p><font size="3">[第1课][<a href="day2_1.html">第2课</a>][<a href="day3_1.html">第3课</a>][<a href="day4_1.html">第4课</a>][<a href="day5_1.html">第5课</a>]</font></p>
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