Javascript cannot find hidden Field in ASP.NET?

I am trying save the disabled property value of a hidden field to track the disabled state of a button between postbacks, with the following javascript

function TrackState(buttonID)
{
   var trackingField = document.getElementById("_tracking" + buttonID);

    return false; // prevent default action
}

HTML

<input type="hidden" name="_trackingButton1" value="true" />

but开发者_运维百科 trackingField seems to be null each time, what is going wrong here

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You need to assign the id property of your element (not just name) and it should work like this:

<input type="hidden" id="_trackingButton1" name="_trackingButton1" value="true" />

I hope this helps.

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In your function

function TrackState(buttonID) { }

what is the buttonID value exactly. I hope it is "Button1". And as the function says getElementById the input has the property id with the same value.

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The getElementById() method specifically looks for id values:

<input type="hidden" id="_trackingButton1" name="_trackingButton1" value="true" />