D3 Examples - Line chart labels using textPath

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<!DOCTYPE html>
​
<head>
    <meta charset="utf-8">
    <link href="https://fonts.googleapis.com/css?family=Oxygen" rel="stylesheet">
    <script src="https://d3js.org/d3.v4.min.js"></script>
    <script src="data.js"></script>
    <style>
        body {
            font-family: 'Oxygen', sans-serif;
            font-size: 12px
            margin: 0;
            top: 0;
            right: 0;
            bottom: 0;
            left: 0;
            background: #222222
        }
​
        .line-app {
            fill: none;
            stroke-width: 4px;
        }
    </style>
</head>
​
<body>
    <script>
​
​
​
        const formatDate = d3.timeFormat("%b %y") // Mar 17
        const parseDate = d3.timeParse("%d/%m/%Y") // 1/03/2017
​
        function formatPercentage(n) { return Math.round(n * 100) + "%"; }
​
        appData.forEach(function (d) {
            d.parsedDate = parseDate(d.date)
        })
​
        let nestedData = d3.nest()
            .key(function (d) { return d.app; })
            .entries(appData)
​
        //////////////////////////////////////////////////////////////////
​
        const width = 700
        const height = 500
​
        const margin = { "top": 50, "bottom": 50, "left": 50, "right": 150, }
​
        let xScale = d3.scaleTime()
            .domain(d3.extent(appData, function (d) { return d.parsedDate; }))
            .range([0, width])
​
        let yScale = d3.scaleLinear()
            .domain([0, 0.5])
            .range([height, 0])
​
        let xAxis = d3.axisBottom(xScale)
            
        let yAxis = d3.axisLeft(yScale)
            .ticks(5)
​
        let colour = d3.scaleOrdinal()
            .domain(["Twitter", "Snapchat", "Facebook", "Instagram"])
            .range(["#00aced", "#fffc00", "#3b5998", "#cd486b"])
​
        let backgroundColour = "#222222"
​
        let line = d3.line()
            .x(function (d) { return xScale(d.parsedDate); })
            .y(function (d) { return yScale(d.percentage); })
            .curve(d3.curveCardinal.tension(0.5));
​
        let svg = d3.select("body").append("svg")
            .attr("width", width + margin.left + margin.right)
            .attr("height", height + margin.top + margin.bottom)
​
        let g = svg.append("g")
            .attr("transform", "translate(" + margin.left + "," + margin.top + ")")
​
        //////////////////////////////////////////////////////////////////
​
        let yAxixBoxDate = new Date("1/1/2017")
        let yAxixBoxWidth = 30
        let yAxixBoxHeight = 20
​
        let axes = g.append("g").attr("class", "axes")
​
        let yAxisG = axes.append("g")
            .attr("transform", "translate(0,0)")
            .call(yAxis)
​
        let xAxisG = axes.append("g")
            .attr("transform", "translate(0," + height + ")")
​
        let xTicks = xAxisG.selectAll(".tick")
            .data(nestedData[0].values )
            .enter()
            .append("g")
            .attr("class", "tick")
            .attr("transform", function(d){ return "translate(" + xScale(d.parsedDate) + ",0)"; })
​
        xTicks.append("text")
            .text(function (d) { return formatDate(d.parsedDate); })
            .attr("y", 18)
            .style("text-anchor", "middle")
​
        xTicks.append("line")
            .attr("y1", -height)
            .attr("y2", 1)
​
        yAxisG.selectAll(".tick").selectAll("text")
            .text(function (d) { return formatPercentage(d); })
            .attr("x", xScale(new Date("1/1/2017")))
            .style("text-anchor", "middle")
​
        yAxisG.selectAll(".tick").selectAll("line")
            .attr("x1", 0)
            .attr("x2", width)
​
        yAxisG.selectAll(".tick").append("rect")
            .attr("x", xScale(yAxixBoxDate) - (yAxixBoxWidth/2))
            .attr("y", -(yAxixBoxHeight/2))
            .attr("width", yAxixBoxWidth)
            .attr("height", yAxixBoxHeight)
            .style("fill", backgroundColour)
        
        yAxisG.selectAll(".tick").selectAll("text")
            .text(function (d) { return formatPercentage(d); })
            .attr("x", xScale(new Date("1/1/2017")))
            .style("text-anchor", "middle")
            .raise()
​
        axes.selectAll(".domain").remove()
​
        axes.selectAll(".tick").selectAll("line")
            .style("stroke", "grey")
            .style("stroke-dasharray", "2,2")
            .style("stroke-linecap", "round")
​
        axes.selectAll(".tick").selectAll("text")
            .style("fill", "grey")
​
        //////////////////////////////////////////////////////////////////
​
        let lines = g.append("g").attr("class", "lines")
​
        let app = lines.selectAll("g")
            .data(nestedData)
            .enter()
            .append("g")
            .attr("id", function (d) { return d.key })
​
        lines.select("#Snapchat").raise()
​
        app.append("path")
            .datum(function (d) { return d.values; })
            .attr("d", line)
            .attr("class", "line-app")
            .attr("id", function(d){ return "line-app-" + d[0].app })
                .style("stroke", backgroundColour)
            .style("stroke-width", "18")
            .style("fill", "none")
​
        let textPaths = app.append("text")
            .attr("dy", 5)
            .append("textPath")
            .text(function (d) { 
                    let thisID = "#line-app-" + d.key
                    let pathLength = d3.select(thisID).node().getTotalLength()
                let label = ""
                let n = (pathLength / d.key.length) / 10
                
                for (var i = 0; i < n; i++) { label = label + " " + d.key }
          
                    return label.toUpperCase();
                })
            .attr("xlink:href", function(d){ return "#" + "line-app-" + d.key; }) 
            .style("fill", function (d) { 
                return d3.rgb(colour(d.key)).darker(); 
                })
            
        app.selectAll("circle")
            .data(function (d) { return d.values; })
            .enter()
            .append("circle")
            .attr("cx", function(d){ return xScale(d.parsedDate) })
            .attr("cy", function(d){ return yScale(d.percentage) })
            .attr("r", 9)
            .style("fill", function (d) { return colour(d.app); })
            .style("stroke", backgroundColour)
            .style("stroke-width", 3)
​
        //////////////////////////////////////////////////////////////////
        
        let duration = 200
​
        var animatePathLabel = setInterval(updatePathLabel, duration);
​
        function updatePathLabel() {
​
          textPaths.text(function(d) {
            let t = d3.select(this).text()
            let l = t.length - 1
            let lastChar = t.slice(-1)
            let newLabel = lastChar + t.slice(0, l)
            return newLabel
          })
​
        }
​
​
​
    </script>
</body>
    