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function tempUser(val){

   $("input[name='userid']").each(function() { 

     this.checked = val; 

  });

}

<br>

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<input type='checkbox' onclick="tempUser(this.checked)" />

<input type='checkbox' name="userid" />

<input type='checkbox' name="userid" />

<input type='checkbox' name="userid" />

<input type='checkbox' name="userid" />

<input type='checkbox' name="userid" />

<input type='checkbox' name="userid" />

<input type='checkbox' name="userid" />