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<div id="theTarget">I have been reached</div>

function isScrolledIntoView(elem)
{
    var docViewTop = $(window).scrollTop();
    var docViewBottom = docViewTop + $(window).height();
    var elemTop = $(elem).offset().top;
    var elemBottom = elemTop + $(elem).height();
    return ((elemBottom >= docViewTop) && (elemTop <= docViewBottom) && (elemBottom <= docViewBottom) && (elemTop >= docViewTop));
}

$(window).scroll(function() {
    if(isScrolledIntoView($('#theTarget')))
    {
        alert('visible');
    }
});

$(document).scroll(function(){
    if($(this).scrollTop()>=$('#theTarget').position().top){
        yourActionHere();
    }
})

var divPosition = $("#theTarget").offset().top;

var scrollPosition = window.scrollY;

$('#theTarget').appear(function() {
  $(this).text('Hello world');
});