<!DOCTYPE html>
<html>
     <head>
       <title>Dynamic circle in Leaflet</title>
     </head>
     <body>
       <!-- https://jf-blog.fr/cercle-dynamique-dans-leaflet -->
	<div class="row">
	    <div class="col-xs-6">
		<input type="number" class="kilometres" name="kilometres" min="0" max="100" placeholder="15" value="15" />
		<input type="range" class="range" name="range" min="0" max="100" step="1" value="15" />
	    </div>
	    <div class="col-xs-6">
		<div id="mapid"></div>
	    </div>
	</div>
     </body>
</html>
div.row {
  width: 700px;
  margin: 0 auto;
}

div > input {
  display: block;
  width: 300px;
  margin  : 10px;
}

#mapid {
  height: 250px;
  width: 300px;
}
map();

function map() {
    let set = 10;
    let zoom = 9;
    let circles;
    let entreprise = [43.600000, 1.433333];
    let mymap = L.map('mapid').setView(entreprise, zoom);

    let osmLayer = L.tileLayer('https://{s}.tile.osm.org/{z}/{x}/{y}.png', {
        attribution: '&copy; <a href="https://osm.org/copyright">OpenStreetMap</a> contributors',
        maxZoom: 18
    });

    mymap.addLayer(osmLayer);
    L.marker(entreprise).addTo(mymap);

    // On retranscrit la valeur du input range dans le input Number (et inversement)
    $('.range').on('input', function() {
        set = $(this).val();
        $('.kilometres').val(set);
    });

    $('.kilometres').on('input', function() {
        set = $(this).val();
        $('.range').val(set);
    });

    circles = L.circle(entreprise, 1000*set, {
        color: 'red',
        fillColor: '#f03',
        fillOpacity: 0.5
    }).addTo(mymap);

    $( ".range, .kilometres" ).on('input', function() {
        if(mymap.hasLayer(circles))
            mymap.removeLayer(circles);

        circles = L.circle(entreprise, 1000*set, {
            color: 'red',
            fillColor: '#f03',
            fillOpacity: 0.5
        }).addTo(mymap);
    });
}

External CSS

  1. https://cdnjs.cloudflare.com/ajax/libs/twitter-bootstrap/4.5.0/css/bootstrap.min.css
  2. https://cdnjs.cloudflare.com/ajax/libs/leaflet/1.7.1/leaflet.css

External JavaScript

  1. https://cdnjs.cloudflare.com/ajax/libs/jquery/3.5.1/jquery.min.js
  2. https://cdnjs.cloudflare.com/ajax/libs/leaflet/1.7.1/leaflet.js