apply force to existing nodes

<!DOCTYPE html>    
<head> 
  <meta charset="utf-8">
  <script src="https://d3js.org/d3.v4.min.js"></script>
  <style>
    body { margin:0;position:fixed;top:0;right:0;bottom:0;left:0; }
  </style>
</head>

<body>
  <button id='applyForce' type='button'>Apply Force</button>
</svg>

// set params for force layout
      const manyBody = d3.forceManyBody().strength(1)
      const center = d3.forceCenter().x((width/2)).y((height/2)) 
 
      // define force
      let force = d3.forceSimulation()
        .force('charge', manyBody)
        .force('center', center)
        .force('collision', d3.forceCollide(d => d.r + 0))
        .nodes(sampleData)
      	.on('end', moveNodes);
      
      function moveNodes() {
        d3.selectAll('circle') 
        	.transition()
        	.duration(1000)
          .attr('cx', d => d.x)
          .attr('cy', d => d.y)
      }
    
    }; //applyForce
    
    d3.select('#applyForce')
    	.on('click', () => {
         console.log('clicked')
         applyForce()
      });
    		
  </script>
</body>

https://d3js.org/d3.v4.min.js