brain.js

var list = d3.select("ul").selectAll("li").data(DATA.people);

data.js

// Declare a constant that can keep all your data
var DATA = {};

DATA.people = [
  {
    "name": "Prateek",
    "superpower": "tree"
  },
  {
    "name": "Chris",
    "superpower": "train"
  }
];