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1.3 简单的计算器
下面，请读者同笔者一起分享一个经典的JavaScript代码，即做一个计算器，如图1-25所示。
图1-25 计算器
这个计算器使用网页浏览器打开即可使用，十分方便，读者可以先尝试看看它的结构。其代码如下，加入任意网页代码的<body>区域中即可。
<script language="javascript">
<!-- Hide the script from old browsers --
function compute(obj) //单击等于"="按钮调用的函数；
{obj.expr.value = eval(obj.expr.value)} ) //用js的eval()方法计算name为expr中的公式
var one = '1' //定义变量；
var two = '2'
var three = '3'
var four = '4'
var five = '5'
var six = '6'
var seven = '7'
var eight = '8'
var nine = '9'
var zero = '0'
var plus = '+'
var minus = '-'
var multiply = '*'
var divide = '/'
var decimal = '.'
function enter(obj, string) //type="button"的调用函数
{obj.expr.value += string} //在表单expr的值后面连上相应的字符
function clear(obj)
{obj.expr.value = ''} //清空表单
// --End Hiding Here -->
</script>
<form name="calc">
<table border=1>
<td colspan=4><input type="text" name="expr" size=30 action="compute(this.form)">
<tr>
<td><input type="button" value=" 7 " onClick="enter(this.form, seven)">
<td><input type="button" value=" 8 " onClick="enter(this.form, eight)">
<td><input type="button" value=" 9 " onClick="enter(this.form, nine)">
<td><input type="button" value=" / " onClick="enter(this.form, divide)">
<tr><td><input type="button" value=" 4 " onClick="enter(this.form, four)">
<td><input type="button" value=" 5 " onClick="enter(this.form, five)">
<td><input type="button" value=" 6 " onClick="enter(this.form, six)">
<td><input type="button" value=" * " onClick="enter(this.form, multiply)">
<tr><td><input type="button" value=" 1 " onClick="enter(this.form, one)">
<td><input type="button" value=" 2 " onClick="enter(this.form, two)">
<td><input type="button" value=" 3 " onClick="enter(this.form, three)">
<td><input type="button" value=" - " onClick="enter(this.form, minus)">
<tr><td colspan=2><input type="button"value=" 0 "onClick="enter(this.form,zero)">
<td><input type="button" value=" . " onClick="enter(this.form, decimal)">
<td><input type="button" value=" + " onClick="enter(this.form, plus)">
<tr><td colspan=2><input type="button"value=" = "onClick="compute(this.form)">
<td colspan=2><input type="button" value="AC" size= 3 onClick="clear(this.form)">
</table>
</form>