how to pass query string in javascript

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Javascript

I am using java script to open popup window on click on button. i am stored the value in hidden field and pass the hidden field value as query string. But query string pass the null value. below is my source code.

<input id="btnFamilyMedicalHistoryDetails" type="button" value="Medical History Details"
önclick=" JavaScript:window.open('../../../User/ViewProfile/FamilyMedicalHistory.aspx?ID'=hfFamilyMemberId, 'Medical History Details','height=500,width=500,resizable= yes, scrollbars=yes')"class="btn-1" />

thanks