[javascript] JS: Uncaught TypeError: object is not a function (onclick)

Edit: Here's a JSfiddle

Edit2: The error is on this line: <input type="button" value="totalbandwidthresult" onclick="javascript:totalbandwidth();">

Trying to have a button perform a calculation. The required variables are below, as well as the HTML where

I am getting an error onclick: Uncaught TypeError: object is not a function index.html:71 onclick

Here is my 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;  
}  

The 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();">  

Basically - it seems that there may be something wrong with the syntax I used in the JS - but I'm not sure.

I was able to figure it out by following the answer in this thread: https://stackoverflow.com/a/8968495/1543447

Basically, I renamed all values, function names, and element names to different values so they wouldn't conflict - and it worked!

Since the behavior is kind of strange, I have done some testing on the behavior, and here's my result:

TL;DR

If you are:

• In a form, and
• uses onclick="xxx()" on an element
• don't add id="xxx" or name="xxx" to that element
  • (e.g. <form><button id="totalbandwidth" onclick="totalbandwidth()">BAD</button></form> )

Here's are some test and their result:

Control sample (can successfully call function)

function totalbandwidth(){ alert("Total Bandwidth > 9000Mbps"); }

<form onsubmit="return false;">
  <button onclick="totalbandwidth()">SUCCESS</button>
</form>

Add id to button (failed to call function)

function totalbandwidth(){ alert("Total Bandwidth > 9000Mbps"); }

<form onsubmit="return false;">
  <button id="totalbandwidth" onclick="totalbandwidth()">FAILED</button>
</form>

Add name to button (failed to call function)

function totalbandwidth(){ alert("Total Bandwidth > 9000Mbps"); }

<form onsubmit="return false;">
  <button name="totalbandwidth" onclick="totalbandwidth()">FAILED</button>
</form>

Add value to button (can successfully call function)

function totalbandwidth(){ alert("Total Bandwidth > 9000Mbps"); }

<form onsubmit="return false;">
  <input type="button" value="totalbandwidth" onclick="totalbandwidth()" />SUCCESS
</form>

Add id to button, but not in a form (can successfully call function)

function totalbandwidth(){ alert("Total Bandwidth > 9000Mbps"); }

<button id="totalbandwidth" onclick="totalbandwidth()">SUCCESS</button>

Add id to another element inside the form (can successfully call function)

function totalbandwidth(){ alert("The answer is no, the span will not affect button"); }

<form onsubmit="return false;">
<span name="totalbandwidth" >Will this span affect button? </span>
<button onclick="totalbandwidth()">SUCCESS</button>
</form>