js addLisnter add code example

Example 1: addEventListener

<body style="height: 5000px">
 <style>
    body, /* blink currently has bug that requires declaration on `body` */
    html {
      scroll-snap-type: y proximity;
    }
    .snaptarget {
      scroll-snap-align: start;
      position: relative;
      top: 200px;
      height: 200px;
      background-color: green;
    }
 </style>
 <div class="snaptarget"></div>
</body>

Example 2: addEventListener

<body style="height: 5000px">
 <script>
    function snap(destination) {
        if (Math.abs(destination - window.scrollY) < 3) {
            scrollTo(window.scrollX, destination);
        } else if (Math.abs(destination - window.scrollY) < 200) {
            scrollTo(window.scrollX, window.scrollY + ((destination - window.scrollY) / 2));
            setTimeout(snap, 20, destination);
        }
    }
    var timeoutId = null;
    addEventListener("scroll", function() {
        if (timeoutId) clearTimeout(timeoutId);
        timeoutId = setTimeout(snap, 200, parseInt(document.getElementById('snaptarget').style.top));
    }, true);
 </script>
 <div id="snaptarget" class="snaptarget" style="position: relative; top: 200px; width: 100%; height: 200px; background-color: green"></div>
</body>