Change an element's class when it comes into view.

is-visible.js

/**
 * Change class when element is in view
 */
var elementTop = $(".container").offset().top;

$(window).on("scroll", function updateClassWhenInView() {
    if ($(window).scrollTop() > elementTop - window.innerHeight * 0.9) {
        $(window).off("scroll", updateClassWhenInView);
        $(".element").removeClass("is-hidden").addClass("is-visible");
    }
});