Question

function CheckavailOnload()
{
  var elems = document.getElementsByClassName('box-collateral box-related');
  var av = document.getElementsByClassName('availability in-stock');
  var x;
  for (var i = 0; i < elems.length; i++)
  {
    if (getComputedStyle(elems[i]).visibility == 'visible') 
    {
      for (var j = 0; j < av.length; j++)
      {
        av[j].style.visibility = 'visible';
        if(elems[i].offsetTop < 0)
        {
          var x = (elems[i].offsetHeight + (elems[i]).offsetTop).toString() + "px";
          alert(x);
        }
        for(m = 0;m < av.length; m++)
        {
          av[m].style.Bottom = (-x);
          return;
        }
       }
     }
   }
   for (var k = 0; k < av.length; k++)
   {
     av[k].style.visibility = 'hidden';
   }
   var divs = document.getElementsByClassName('add-to-cart');
   for(var l = 0; l < divs.length; l++)
   { 
     divs[l].style.marginTop = (-500).toString() + "px";
     divs[l].style.marginLeft = (-20).toString() + "px";
   }
}
window.onload = CheckavailOnload;

here i am trying to move a paragraph tag have baground image depending upon the div offsetTop and Offset height div also have bacground image i am moving para tag just below the div but addition of offsetHeight and offsetTop is coming NAN please anyone can help me

Answer 1

You’ve declared var x; at the beginning of your script. Then later you’re checking:

if(elems[i].offsetTop < 0) {
    var x = (elems[i]...); // var is not recommended to be here, x has been already declared once
}

If elems[i].offsetTop happens to be >= 0, x will be undefined in this line:

av[m].style.Bottom = (-x); // Notice a typo here: should be av[m].style.bottom

This last expression gives you NaN. To avoid this, you need to either assign a default value to x in the beginning of the script, or add an else statement after the if wherein some numeric value is assigned to x.

Also return in the for...m-loop seems to break your code, the loop will never finish the job and the rest of the code will be never executed.

Using (-500).toString() + "px"; feels complex, why not just use "-500px";?