isVisibleOnScreen.js

//this script requires jQuery
function isVisibleOnScreen(target){
  var depth = $(target).offset().top; //depth from the top
  var targetHeight = $(target).height(); //height of the target element
  var winHeight = $(window).height(); //current window height
  var totalTargetDepth = parseInt(targetHeight)+parseInt(depth)+winHeight; //total depth
  var scrolledDepth = $(window).scrollTop(); //how far you scrolled
  var elmVisible = winHeight+scrolledDepth; //the point where the target starts displaying at the bottom of the screen
  //console.log(scrolledDepth+'-'+elmVisible+'-'+depth);
  //runs the logic condition
  if(elmVisible >= depth && elmVisible < totalTargetDepth){
      return true;
  }else{
      return false;
  }   
}
//usage
var myTarget = $('.selector'); //grab the selector
//use it..
if(isVisibleOnScreen(myTarget) == true){
  console.log('Visible On Screen');
}else{
  console.log('Not visible on screen');
}

//Enjoy!