Chapter 08Tooltips

A tooltip is a box (usually containing some descriptive text) that appears when the user hovers over an element on the page and disappears when the user moves the mouse off the element.

To create a tool tip we need a div. The div will be that box that holds the text. Below, we create a div, give it the class name tooltip, and make it transparent.

var tooltip ="body")
  .attr("class", "tooltip")
  .style("opacity", 0);

The tooltip class sets a number of style properties including, and perhaps most importantly, the position property. The position property is set to absolute allowing us to change the box’s position dynamically in JavaScript using the left and top properties.

  .tooltip {
    position: absolute;
    text-align: center;
    padding: 2px;
    font: 12px sans-serif;
    background: lightsteelblue;
    border: 0px;
    border-radius: 8px;
    pointer-events: none;
  .box {
    width: 580px;
    height: 100px;
    background: lightblue;

We then register handers for the mouseover and mouseout events.  When the user hovers over the blue box below we transition the tooltip to visible using the opacity property, set its text with the html method, and move it to a location near the mouse click using the left and top properties.  When the user moves off the code segments, we make the tooltip transparent again.

var tooltip ="body")
    .attr("class", "tooltip")
    .style("opacity", 0);

  .on("mouseover", function(d) {
        .style("opacity", .9);
     tooltip.html("Happy Birthday!")
        .style("left", (d3.event.pageX) + "px")
        .style("top", (d3.event.pageY - 10) + "px");
  .on("mouseout", function(d) {
        .style("opacity", 0);

<div class="box"></div>