我在JS代码中哪里做错了什么

Question

I am stuck why this code is not working. Why Image position not fixed when i scroll down the window.

I know this is a very common question help would be appreciated.

 $(window).scroll(function () { if($(window).scrollTop() === 200){ $("#dataImg").css({'position':'fixed','top':'0px'}); } }); 

 .container { height: 1500px; background: #000; } 

 <script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script> <div class="container"> <img src="http://www.placehold.it/200x300" id="dataImg"> </div> 

Answer 1

I think the problem is with the "$(window).scrollTop === 200". You want to use > or < depending on your situation like this:

$(window).scroll(function () {
  if($(window).scrollTop() > 200){
    $("#dataImg").css({'position':'fixed','top':'0px'});
  }
});

Answer 2

I suppose you want to fix that image when you scroll down over 200px. You can change your Javascript code to following:

$(window).scroll(function () {
    if($(window).scrollTop() >= 200){
      $("#dataImg").css({'position':'fixed','top':'0px'});
    } else {
      $("#dataImg").css({'position': '', 'top' : ''});
    }
});