Enqueue script, taking no effect [closed]

Try this to set the alert if you’ve scrolled 100px from the top of the page.

jQuery(document).ready(function ($) {
    $(window).scroll(function(){
        var ScrollTop = parseInt($(window).scrollTop());

        if (ScrollTop > 100) {
            alert("You've scrolled 100 pixels.");
        }
    });
});

Here is a JSFiddle showing it in action.

Assuming you want to do more than just show an alert, here would be how you add a class of “scroll” to an element with the class of “site-header” and have it removed when you are less than 100px from the top of the browser window:

jQuery(document).ready(function ($) {
    $(window).scroll(function(){
        var ScrollTop = parseInt($(window).scrollTop());

        if (ScrollTop > 100) {
            $( ".site-header" ).addClass( "scroll" );
        }else{
            $( ".site-header" ).removeClass( "scroll" );
        }

    });
});