jQuery scrollTop function

I have one page where the next page is fired when the user reaches the bottom of the page:

$(window).scroll(function(){
    if  ($(window).scrollTop() == $(document).height() - $(window).height()){
        next_funtion();
    }
});

However, I want next page to be fired when the user reaches 50% of the page height or 200 px fro开发者_高级运维m the top.

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It's basic math. Without it, jQuery ain't gonna help you at all:

$(window).scroll(function() {
  if (($(window).scrollTop() < 200) || ($(window).scrollTop() < $(document).height() / 2)) {
    next_funtion();

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You can try this code for ScrollTop Function

$('html,body').animate({

      scrollTop: $('#'+id_name).offset()

    }, "fast");