javascript - 使用下拉菜单/单选按钮选择舍入值

Question

这包含两个问题。第一个问题是将数字四舍五入到某个小数点。第二个问题是将下拉菜单连接到正确的小数点。

首先是我的代码:

<style>
  span{font-style:italic;}
  span{color:green;}
</style>

<script>
    function calcul(){
            var sales = parseFloat(document.getElementById("sales").value);
            var OpExp = parseFloat(document.getElementById("OpExp").value);
            var TaxAll = parseFloat(document.getElementById("TaxAll").value);
            var Depre = parseFloat(document.getElementById("Depre").value);
            var Divid = parseFloat(document.getElementById("Divid").value);
            var TaxR = parseFloat(document.getElementById("TaxR").value);
            //GP = Gross Profit
            var GP = sales - OpExp;
            //TaxInc = Taxable Income
            var TaxInc = GP + TaxAll;
            //NetInc = Net Income
            var NetInc = TaxInc - ((TaxR / 100) * TaxInc);
            document.getElementById("NetIncome").innerHTML= 
            TaxInc - ((TaxR / 100) * TaxInc);
            //AtRE = Addition to Retained Earnings
            document.getElementById("AtRE").innerHTML = NetInc - Divid;
        }
</script>

<form action="" id="nothing">
In 2007 the British building firm Balfour Betty plc had sales of 
<input type="text" id="sales" maxlength="6" size="6"> 
million, total operating expenses of 
<input type="text" id="OpExp" maxlength="6" size="6"> 
million, a tax allowance (rebate) of 
<input type="text" id="TaxAll" maxlength="6" size="6"> 
million because of past losses, and 
<input type="text" id="Depre" maxlength="6" size="6"> 
depreciation. <strong>What is the net income of the
firm?</strong><br />
<br />
Balfour Betty plc paid out <input type="text" id="Divid" maxlength="6" size="6"> million 
in cash dividends. <strong>What is the addition to retained earnings?</strong><br />
<br />
The tax rate is <input type="text" id="TaxR"  maxlength="6" size="6"> %.<br />
<br />
  <input type="button" value="Calculate" id="but" onclick="calcul()" /><br />
<br />
</form>

<strong>The Net Income of Balfour Betty plc is </strong><span id="NetIncome">XXX</span>
<strong> million</strong><br />
<br />
<strong>The addition to retained earnings of Balfour Betty plc is </strong><span id="AtRE">
XXX</span><strong> million</strong>
<br />
<br />

第一个问题:四舍五入数字。答案如下:<span id="NetIncome">需要动态舍入。我尝试添加一个名为 RNetInc 的新变量并添加以下方程 RNetInc = NetInc.toFixed(4) ，但它只给了我两位小数，刷新后它甚至不再工作了。将答案四舍五入到小数点后 N 位的最佳方法是什么？

第二个问题我不知道是否可能。我的想法如下: 下拉菜单

<select>
    <option value"1">1 decimal</option>
    <option value"2">2 decimals</option>
    <option value"3">3 decimals</option>
</select> 

所以，我想要的是当我点击 N decimal 时，答案将更改为小数 N。这是一种非常复杂的情况，但我经常需要这种情况。

由于我只了解 Javascript 的(非常)基础知识，即使使用 Google 我也找不到答案。有人能让我走上正轨吗(如果可能的话)？提前致谢。

Answer 1

我建议仅修复最终结果，toFixed()返回一个字符串。

用于选择的HTML:

<select id="dec">
    <option value="1">1 decimal</option>
    <option value="2">2 decimals</option>
    <option value="3">3 decimals</option>
</select>

在calcul()中:

var decs = +(document.getElementById('dec').value); // Add this line
document.getElementById("NetIncome").innerHTML = (TaxInc - ((TaxR / 100) * TaxInc)).toFixed(decs);
document.getElementById("AtRE").innerHTML = (NetInc - Divid).toFixed(decs);

A live demo at jsFiddle (已更新)。

编辑

看来我部分误解了你的问题。请检查更新的 fiddle ，现在您还可以通过从 select 中选择一个值来随时更改小数位数。