如何使用javascript通过id隐藏html div(how to hide an html div by id using javascript)

 我试图用Javascript隐藏HTML div并且收到错误 
 
 
 
 JavaScript运行时错误：无法获取未定义或空引用的属性“样式” 
 
 
 这是我的JavaScript代码： 
 
if (typeof(jsondata[0]) == 'undefined') {
    alert('should be hidden');
    document.getElementById("unassignedDevices").style.visibility = "hidden";
}
 
 这是我的HTML： 
 
<div id="unassignedDevices">
    <button id="unassignedDevicesbutton" class="button-basicmenu" onclick="findUnassignedDevices();">Find unassigned Devices</button>

    <table id="gridunassignedDevices"></table>

</div>
 
 因此，当我开始调试时，页面警报'应该被隐藏'然后我得到JavaScript运行时错误。 
 
 我怎么能隐藏这个div？ 

I am trying to hide an HTML div with Javascript and am getting an error
 
 
 
JavaScript runtime error: Unable to get property 'style' of undefined or null reference
 
 
Here is my JavaScript code:
 
if (typeof(jsondata[0]) == 'undefined') {
    alert('should be hidden');
    document.getElementById("unassignedDevices").style.visibility = "hidden";
}
 
and here is my HTML:
 
<div id="unassignedDevices">
    <button id="unassignedDevicesbutton" class="button-basicmenu" onclick="findUnassignedDevices();">Find unassigned Devices</button>

    <table id="gridunassignedDevices"></table>

</div>
 
So when I start debugging, the page alerts 'should be hidden' and then I get the JavaScript runtime error.
 
How can I hide this div?

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