D3.js snippet to help understand enter/update/exit good tutorial here: http://mbostock.github.com/d3/tutorial/circle.html

D3 test.js

//select p tags to manipulate
d3.select("body").selectAll("p")

//initial dataset
      .data([4, 8, 15, 16, 23, 42])

//create any nodes that don't already exist (all of them)
      .enter().append("p")

//set the node text based on the data
      .text(function(d) { return "I’m number " + d + "!";}) 

//updated dataset (note: the length is shorter)
      .data([4, 15, 23, 8, 57])

//set the node text based on the updated data
    .text(function(d) { return "I’m number " + d + "!"; })

//also modify some styles this time
    .style("font-size", function(d) { return d + "px"; })
      
    .style("text-decoration","line-through")

//finished
    .exit()
//remove the nodes no longer needed
    .remove();