JSFiddle - React, Tailwind, and code Playground

HTML

<div id="menu">
	<a href="#" divToShow="contenue1">Menu du contenue 1</a>
    <a href="#" divToShow="contenue2">Menu du contenue 2</a>
    <a href="#" divToShow="contenue3">Menu du contenue 3</a>
</div>
<div id="monSite">
	<div id="contenue1" class="show">Contenue de mon site n°1 !</div>
    <div id="contenue2" style="display:none;">Contenue de mon site n°2 !</div>
    <div id="contenue3" style="display:none;">Contenue de mon site n°3 !</div>
</div>

JavaScript

$( "#menu a" ).click(function() {
    elementToFadeIn = $(this).attr('divToShow');
  	$('.show').fadeOut(function(){
        $(this).removeClass('show');
        $('#'+elementToFadeIn).fadeIn(function(){
            $(this).addClass('show');
        });
    });
});