Health and Wealth with tooltip

<!DOCTYPE html>
<head>
    <meta charset="utf-8">
    <script src="https://d3js.org/d3.v4.min.js"></script>
    <script src="https://cdnjs.cloudflare.com/ajax/libs/d3-tip/0.9.1/d3-tip.min.js"></script>
    <script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script>
    
    <link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.2/css/bootstrap.min.css">
    
    <script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.2/js/bootstrap.min.js"></script>
    <style>

#chart-area svg {
           margin-left: auto;
           margin-right: auto;
           display: block;
       }

#reset-button, #play-button {
           float: left;
           margin-right:10px;
       }

#reset-button, #play-button {
           margin-top: 5px;
           margin-bottom:10px;
       }
  
    </style>
</head>

<body>
<div class="container">
    <div class="row">
        <div class="col-md-6">
            <button id="play-button" class="btn btn-primary">Play</button>
            <button id="reset-button" class="btn btn-primary">Reset</button>
        </div>
    </div>
    <div class="row">
        <div class="col-md-12">
            <div id="chart-area"></div>
        </div>
    </div>
</div>
  <script>
    var margin = { left:80, right:20, top:50, bottom:100 };
    var height = 600 - margin.top - margin.bottom,
        width = 900 - margin.left - margin.right;

var g = d3.select("#chart-area")
        .append("svg")
        .attr("width", width + margin.left + margin.right)
        .attr("height", height + margin.top + margin.bottom)
        .append("g")
        .attr("transform", "translate(" + margin.left +
            ", " + margin.top + ")");

var time = 0;
    
    // Tooltip
    var tip = d3.tip().attr('class', 'd3-tip')
       .html(function(d) {
          var text = "<strong>Country:</strong> <span style='color:red'>" + d.country + "</span><br>";
        text += "<strong>Continent:</strong> <span style='color:red;text-transform:capitalize'>" + d.continent + "</span><br>";
        text += "<strong>Life Expectancy:</strong> <span style='color:red'>" + d3.format(".2f")(d.life_exp) + "</span><br>";
        text += "<strong>GDP Per Capita:</strong> <span style='color:red'>" + d3.format("$,.0f")(d.income) + "</span><br>";
        text += "<strong>Population:</strong> <span style='color:red'>" + d3.format(",.0f")(d.population) + "</span><br>";
        return text;
    });
    
    g.call(tip);
    
    var interval;
    var formattedData;
    //Labels
    var xLabel = g.append("text")
        .attr("y", height + 50)
        .attr("x", width / 2)
        .attr("font-size", "20px")
        .attr("text-anchor", "middle")
        .text("GDP Per Capita ($)");
    var yLabel = g.append("text")
        .attr("transform", "rotate(-90)")
        .attr("y", -40)
        .attr("x", -170)
        .attr("font-size", "20px")
        .attr("text-anchor", "middle")
        .text("Life Expectancy (Years)")
    var timeLabel = g.append("text")
        .attr("y", height -10)
        .attr("x", width - 40)
        .attr("font-size", "40px")
        .attr("opacity", "0.4")
        .attr("text-anchor", "middle")
        .text("1800");
    //Scales
    var x = d3.scaleLog()
        .base(10)
        .domain([142, 150000])
        .range([0, width]);

var y = d3.scaleLinear()
        .domain([0, 90])
        .range([height, 0]);

var area = d3.scaleLinear()
        .range([25*Math.PI, 1500*Math.PI])
        .domain([2000, 1400000000]);

// X Axis
    var xAxisCall = d3.axisBottom(x)
        .tickValues([400, 4000, 40000])
        .tickFormat(d3.format("$"));
    g.append("g")
        .attr("class", "x axis")
        .attr("transform", "translate(0," + height +")")
        .call(xAxisCall);

// Y Axis
    var yAxisCall = d3.axisLeft(y)
        .tickFormat(function(d){ return +d; });
    g.append("g")
        .attr("class", "y axis")
        .call(yAxisCall);
    var continentColor = d3.scaleOrdinal(d3.schemeCategory20);
    
   //Building the Legend
    var continents = ["europe", "asia", "americas", "africa"];

var legend = g.append("g")
        .attr("transform", "translate(" + (width - 10) +
            "," + (height - 125) + ")");

continents.forEach(function(continent, i){
        var legendRow = legend.append("g")
            .attr("transform", "translate(0, " + (i * 20) + ")");

legendRow.append("rect")
            .attr("width", 10)
            .attr("height", 10)
            .attr("fill", continentColor(continent));

legendRow.append("text")
            .attr("x", -10)
            .attr("y", 10)
            .attr("text-anchor", "end")
            .style("text-transform", "capitalize")
            .text(continent);
    });

//GET THE DATA
    d3.json("data.json", function(data){
        console.log(data);

// Clean data
         formattedData = data.map(function(year){
            return year["countries"].filter(function(country){
                var dataExists = (country.income && country.life_exp);
                return dataExists
            }).map(function(country){
                country.income = +country.income;
                country.life_exp = +country.life_exp;
                return country;
            })
        });
       
        // First run of the visualization
        update(formattedData[0]);
    });

$("#play-button")
        .on("click", function(){
            var button = $(this);
            if (button.text() == "Play"){
                button.text("Pause");
                interval = setInterval(step, 100);
            }
            else {
                button.text("Play");
                clearInterval(interval);
            }
        })

$("#reset-button")
        .on("click", function(){
            time = 0;
            update(formattedData[0]);
        })

function step(){
        // At the end of our data, loop back
        time = (time < 167) ? time+1 : 0
        update(formattedData[time]);
    }

function update(data) {

var t = d3.transition()
            .duration(100);

// JOIN new data with old elements.
        var circles = g.selectAll("circle")
            .data(data, function(d) {return d.country; });

// EXIT old elements not present in new data.
        circles.exit()
            .attr("class", "exit")
            .remove();

// ENTER new elements present in new data.
        var enter = circles.enter()
            .append("circle")
            //.filter(function(year) {return year === "1800"})
            .attr("class", "enter")
            .attr("fill", function(d) { return continentColor(d.continent); })
            .on("mouseover", tip.show)
            .on("mouseout", tip.hide)
            .merge(circles)

.transition(t)
              .attr("cy", function(d){ return y(d.life_exp); })
              .attr("cx", function(d){ return x(d.income) })
              .attr("r", function(d){ return Math.sqrt(area(d.population) / Math.PI) });

// Update the time label
        timeLabel.text(+(time + 1850))
    }

</script>
</body>

https://d3js.org/d3.v4.min.js

https://cdnjs.cloudflare.com/ajax/libs/d3-tip/0.9.1/d3-tip.min.js

https://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js

https://maxcdn.bootstrapcdn.com/bootstrap/3.3.2/js/bootstrap.min.js