javascript - Styling d3´s tooltip

Question

I implement a tooltip over circles placed through d3 on a leafletmap like this:

var tooltip = d3.select("body")
    .append("div")
    .attr("id", "mytooltip")
    .style("position", "absolute")
    .style("z-index", "10")
    .style("visibility", "hidden")
    .text("a simple tooltip");



feature.on("mouseover",function(d) { 
    d3.select(this)
    .transition()
    .ease("elastic")
    .duration(500)
    .attr('r', function (d){ 
        return (d.properties.xy * 5)
        .style("stroke", "black")
        d3.select("#mytooltip")
            .style("visibility", "visible")
            .text(d.properties.xy1 + " " + d.properties.xy2)
    });

feature.on("mousemove", function() {
    return tooltip.style("top", (d3.event.pageY-10)+"px")
    .style("left",(d3.event.pageX+10)+"px");

    });

feature.on("mouseout",function(d) { 
    d3.select(this)
    .transition()
    .ease("elastic")
    .duration(500)
    .attr('r', function (d){ 
            return (d.properties.xy);
        })
        .style("stroke", "none")
        d3.select("#mytooltip")
            .style("visibility", "hidden")
    });

Where my feature is this:

var feature = g.selectAll("circle")
      .data(myData.features)
      .enter()
      //...

I wonder how I can style the tooltip that shows up? Is there a way to give it a background, write something in bold, italic, different colors etc?

Answer 1

This is what I like to do. First, I set the CSS style for the tooltip, using a div with a class named "tooltip":

div.tooltip {   
    position: absolute;         
    etc...          
}

Then I set a tooltip var (here, svgId is the ID of the element where you append your SVG, not much different of selecting "body" as you did):

var tooltip = d3.select("#svgId").append("div") 
    .attr("class", "tooltip")               
    .style("opacity", 0);

The div has 0 opacity. Then it's just a matter of showing the tooltip on mouseover or mousemove:

selection.on("mousemove", function(d) {
    tooltip.html("<strong> Look, I'm bold !</strong> and now I'm not bold<br>
        and this is another line!and this is my data: " + d.whatever)
        .style('top', d3.event.pageY - 12 + 'px')
        .style('left', d3.event.pageX + 25 + 'px')
        .style("opacity", 1);
});

You can use HTML tags to style your text inside the tooltip, making it bold, italic etc. And, finally, we make the tooltip disappear on mouseout (as you did):

selection.on("mouseout", function(d) {
    tooltip.style("opacity", 0);
});

Since the div with 0 opacity still takes space in the page, a better approach is changing its display property from none to block during the mouseover, and back to none in the mouse out.