JavaScript: XML DOM Load Error -

i have problem load xml file (xml dom load),using javascript so,whene this:

var xmlfile=loadxmldoc("test.xml"); 

it load correct , can use , exploit it. whene spécifie xml filename load input value(xml filename load=input value) this: dosn't work , need solution please

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... var usr = document.getelementbyid('user').value+".xml";   //exemple:if (input id="user" value)="test", result "test.xml" var xmlfile=loadxmldoc(usr);   //load "test.xml" file ... 

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its dosn't work , need solution please