const let eg

<!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>

<br>
  <h3> const and let with map and push  </h3>  
  <script>
    "use strict";
    
    const james = [55];
    
    let james1 = JSON.parse(JSON.stringify(james));  // why?????????
    // could use other things too:
    //https://stackoverflow.com/questions/728360/how-do-i-correctly-clone-a-javascript-object
    
    let james2 = james.map( (x) => x*5 )
    
    let james3 = james.push(46)
    
    
    const svg = d3.select("body").append("svg")
      .attr("width", 960)
      .attr("height", 500)
    
    svg.append("text")
      .text("your number was: "+ james + " or " +
            james1 + " or "  +
            james2 + " or " + james3)
      .attr("y", 200)
      .attr("x", 120)
      .style("font-size", 36)
      .style("font-family", "monospace")

</script>
</body>

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