functions.js

// You filter array data with a anonymous function passed to `filter`
[1,2,3,4,5,6].filter(function(el) {return el >= 4});

// In this example, we make the html of the div, a function of the data 
// in the array. We do this using an anonymous function.
d3.select(“div”).data([1,2,3,4]).enter().append("div")
  .html(function (d) {return d});
  
//  In the below anonymous function, the d argument references the data bound to that div. 
// There is a second argument i that references the index, if needed.
d3.select(“div”).data([1,2,3,4])
  .enter()
  .append("div")
  .attr(“cx”, function(d, i) { return i})

// You can add interactivity through events.
d3.select(“div”)
  .style(“background-color”, “pink”)
  .on(“click”, function() { console.log("You clicked a div") });