JS：未捕获类型错误：对象不是函数（onclick）

Edit: 这是一个 JSfiddle http://jsfiddle.net/XpmZG/

Edit2:错误在这一行：<input type="button" value="totalbandwidthresult" onclick="javascript:totalbandwidth();">

尝试让按钮执行计算。所需的变量如下，以及 HTML，其中

我在点击时遇到错误：Uncaught TypeError: object is not a function index.html:71 onclick

这是我的 JavaScript

function totalbandwidth() {  
    var fps=Number(document.calculator.fps.value);  
    var bitrate=Number(document.calculator.bitrate.value);  
    var numberofcameras = Number(document.calculator.numberofcameras.value); 
    var encoding = document.calculator.encoding.value; 
    if (encoding = "mjpeg")
    {
        storage = bitrate*fps;
    }
    else
    {
        storage = bitrate;
    }

    totalbandwidth = (numberofcameras * storage) / 1000;
    document.calculator.totalbandwidthresult.value = totalbandwidth;  
}  

HTML：

<form name="calculator" class="formtable">  
<div class="formrow"><label for="rcname">RC Name</label> <input type="text" name="rcname"></div>  
<div class="formrow"><label for="fps">FPS</label> <input type="text" name="fps">  </div>  
<div class="formrow"><label for="bitrate">Bitrate</label> <input type="text" name="bitrate">  </div>  
<div class="formrow"><label for="numberofcameras">Number of Cameras</label> <input type="text" name="numberofcameras"> </div>   
<div class="formrow"><label for="encoding">Encoding</label> <select name="encoding" id="encodingoptions">
  <option value="h264">H.264</option>
  <option value="mjpeg">MJPEG</option>
  <option value="mpeg4">MPEG4</option>
</select></div>  
Total Storage: <input type="text" name="totalstorage">   
Total Bandwidth: <input type="text" name="totalbandwidth">   
<input type="button" value="totalbandwidthresult" onclick="javascript:totalbandwidth();">  

基本上 - 似乎我在 JS 中使用的语法可能有问题 - 但我不确定。

请仅更改函数名称；无需其他更改

<script>
    function totalbandwidthresult() {
        alert("fdf");
        var fps = Number(document.calculator.fps.value);
        var bitrate = Number(document.calculator.bitrate.value);
        var numberofcameras = Number(document.calculator.numberofcameras.value);
        var encoding = document.calculator.encoding.value;
        if (encoding = "mjpeg") {
            storage = bitrate * fps;
        } else {
            storage = bitrate;
        }

        totalbandwidth = (numberofcameras * storage) / 1000;
        alert(totalbandwidth);
        document.calculator.totalbandwidthresult.value = totalbandwidth;
    }
</script>

<form name="calculator" class="formtable">
    <div class="formrow">
        <label for="rcname">RC Name</label>
        <input type="text" name="rcname">
    </div>
    <div class="formrow">
        <label for="fps">FPS</label>
        <input type="text" name="fps">
    </div>
    <div class="formrow">
        <label for="bitrate">Bitrate</label>
        <input type="text" name="bitrate">
    </div>
    <div class="formrow">
        <label for="numberofcameras">Number of Cameras</label>
        <input type="text" name="numberofcameras">
    </div>
    <div class="formrow">
        <label for="encoding">Encoding</label>
        <select name="encoding" id="encodingoptions">
            <option value="h264">H.264</option>
            <option value="mjpeg">MJPEG</option>
            <option value="mpeg4">MPEG4</option>
        </select>
    </div>Total Storage:
    <input type="text" name="totalstorage">Total Bandwidth:
    <input type="text" name="totalbandwidth">
    <input type="button" value="totalbandwidthresult" onclick="totalbandwidthresult();">
</form>