JSFiddle - React, Tailwind, and code Playground

HTML

There is an orange div lower on the screen.  Click any box to alert if the orange box is within the visible viewport.

<div class="box orange" id="boxorange"></div>
<div class="box"></div>
<div class="box"></div>
<div class="box"></div>
<div class="box"></div>
<div class="box"></div>
<div class="box"></div>
<div class="box"></div>
<div class="box"></div>
<div class="box"></div>

CSS

.box {
    width: 200px;
    height: 200px;
    margin-bottom: 10px;
    background: blue;    
}
.orange {
    background: orange;   
}

JavaScript

$.fn.isOnScreen = function(){
    
    var win = $(window);
    
    var viewport = {
        top : win.scrollTop(),
        left : win.scrollLeft()
    };
    viewport.right = viewport.left + win.width();
    viewport.bottom = viewport.top + win.height();
    
    var bounds = this.offset();
    bounds.right = bounds.left + this.outerWidth();
    bounds.bottom = bounds.top + this.outerHeight();
    
    return (!(viewport.right < bounds.left || viewport.left > bounds.right || viewport.bottom < bounds.top || viewport.top > bounds.bottom));
    
};

$(window).scroll(function(){
    if($('#boxorange').isOnScreen() == true){
    	$('#boxorange').css({"height":"400px"}); 
   	  $('#boxorange').css({"width":"400px"}); 
    } else{
			$('#boxorange').css({"height":"200px"}); 
    	$('#boxorange').css({"width":"200px"});     }
});