jq page scroll event listener

    $(document).scroll(function() {
        var scroH = $ (document) .scrollTop (); // Roll Height
        var viewH = $ (window) .height (); // visible height 
        var contentH = $ (document) .height (); // height content
 
        if (scroH> 100) {// from the top is larger than 100px
 
        }
        if (contentH - (scroH + viewH) <= 100) {// is smaller than the height from the bottom 100px
             
        }  
        if (contentH = (scroH + viewH)) {// scroll bar to the bottom it
             
        }  
 
    });