getElementById

function addData(value1){
    if(document.getElementById('li'+value1).checked==true){
       if(document.getElementById(value1).value==""){
          document.getElementById(value1).value=1;
       }
    }
}

<script>
var mnumber = document.getElementById('mobileno').value;
if(mnumber.length >=10) {
    alert("Mobile Number Should be in 10 digits only");
    document.getElementById('mobileno').value = "";
    document.getElementById('mobileno').focus();
    return false;
}
http://stackoverflow.com/questions/4801655/
function focusOnElement(element_id) {
     $('#div_' + element_id).goTo(); // need to 'go to' this element
}
<div id="div_element1">
   yadda yadda
</div>
<div id="div_element2">
   blah blah
</div>
<span onclick="focusOnElement('element1');">Click here to go to element 1</span>
<span onclick="focusOnElement('element2');">Click here to go to element 2</span>
============================
https://cgd.io/2008/using-javascript-to-scroll-to-a-specific-elementobject/
//Finds y value of given object
function findPos(obj) {
    var curtop = 0;
    if (obj.offsetParent) {
        do {
            curtop += obj.offsetTop;
        } while (obj = obj.offsetParent);
    return [curtop];
    }
}
//Get object
var SupportDiv = document.getElementById('customer_info');

//Scroll to location of SupportDiv on load
window.scroll(0,findPos(SupportDiv));