enter exit merge

<!DOCTYPE html>
<head>
  <meta charset="utf-8">
  <script src="https://d3js.org/d3.v5.min.js"></script>
  <style>
    body { margin:0;position:fixed;top:0;right:0;bottom:0;left:0; }
  </style>
</head>

<body>
  <script>
    // Feel free to change or delete any of the code you see in this editor!
    var svg = d3.select("body").append("svg")
      .attr("width", 960)
      .attr("height", 500)
     
    const radius = 100;
    
    var sheepData = [
      {color: "purple", radius, x: 10, y: radius, name: "purple"},
      {color: "red", radius, x: 10, y: radius * 2, name: "red"},
      {color: "pink", radius, x: 10, y: radius * 3, name: "pinkie"},
    ] 
    
    const blackSheep = {color: "black", radius: 10, x: 10, y: 100, name: "blacksheep"};
    
    function update(data) {

// DATA JOIN
      // Join new data with old elements, if any.
      var sheep = svg.selectAll("g")
        .data(data);

// UPDATE
      // Update old elements as needed.
      const getColor = d => {
            //console.log("color: ",d)
        return d.color; 
      }
      
      const getTranslate = d => {
       	console.log("trans : ",d)
            
       	return "translate (" + d.x + "," + d.y + ")";
      }
      
      const getClass = d => {
        return d.name; 
      }
      // sheep.attr("transform", getTranslate);

// ENTER
      // Create new elements as needed.
      //
      // ENTER + UPDATE
      // After merging the entered elements with the update selection,
      // apply operations to both.
      let sheepG = sheep.enter().append("g")
      							.attr("transform", getTranslate)
      							.attr("class", getClass);
      
      
      sheepG
          			.append("circle") // ENTER
                	.attr("r", d => d.radius)
                	.style("fill", getColor);
      const getEase = () => {
        const coinFlip = Math.random() * 100;
        return (coinFlip > 50) ? d3.easeSin : d3.easeBack;
      }
      
      
      sheep
        .merge(sheep)
      		.transition()
      			.ease(getEase())
      			.delay(500)
      			.duration(2000)
          	.attr("transform", getTranslate);
      
   
      // EXIT
      // Remove old elements as needed.
      sheep.exit().remove();
		}
          
    update(sheepData);
    
    let count = 0;
    
    let int = setInterval( () => {
      //sheepData.push(blackSheep);
      
      function createNewSheep(sheep){
        if (sheep.name === 'pinkie') return sheep;
        
        const newX = sheep.x + ( radius * count); 
        //console.log("newX: ", newX);
        
        return {...sheep, x: newX}; 
      }
      
      const newSheepData = sheepData.map(createNewSheep);
        
      update(newSheepData);
      if (count > 10) {
        clearInterval(int);
      }	
      count++;
    }, 1000)
    
  </script>
</body>

https://d3js.org/d3.v5.min.js